Sample records for magnetic anisotropy field

The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magneticfield and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave numbers.

Magneticanisotropy in Fe-25Cr-12Co-1Si alloy induced by external magneticfield ZHEN Liang( )1 properties of Fe-25Cr-12Co-1Si alloy thermo-magnetically treated under different external magneticfield of external magneticfield during isothermal magnetic ageing. Approximately 28% of the total coercivity can

The natural occurrence of small scale structures and the extreme anisotropy in the evolution of a magneticfield embedded in a conducting flow is interpreted in terms of the properties of the local Lyapunov exponents along the various local characteristic (un)stable directions for the Lagrangian flow trajectories. The local Lyapunov exponents and the characteristic directions are functions of Lagrangian coordinates and time, which are completely determined once the flow field is specified. The characteristic directions that are associated with the spatial anisotropy of the problem, are prescribed in both Lagrangian and Eulerian frames. Coordinate transformation techniques are employed to relate the spatial distributions of the magneticfield, the induced current density, and the Lorentz force, which are usually followed in Eulerian frame, to those of the local Lyapunov exponents, which are naturally defined in Lagrangian coordinates.

The pressure anisotropy is calculated for a plasma in a bumpy cylindrical magneticfield in the low collisionality (banana) regime for small magnetic-field modulations ({epsilon}{identical_to}{delta}B/2B<<1). Solutions are obtained by integrating the drift-kinetic equation along field lines in steady state. A closure for the local value of the parallel viscous force B{center_dot}{nabla}{center_dot}{pi}{sub parallel} is then calculated and is shown to exceed the flux-surface-averaged parallel viscous force by a factor of O(1/{epsilon}). A high-frequency limit ({omega}>>{nu}) for the pressure anisotropy is also determined and the calculation is then extended to include the full frequency dependence by using an expansion in Cordey eigenfunctions.

We investigate the transitions of spin configurations in ultrathin nanostructures by tuning the perpendicular anisotropy (K{sub z}) and out-of-plane magneticfield (H), using the Monte Carlo simulation. It is revealed that enhancing the anisotropy K{sub z} can drive the evolution of in-plane vortex state into intriguing saturated magnetization states under various H, such as the bubble domain state and quadruple-block-domain state etc. The spin configurations of these states exhibit remarkable H-dependence. In addition, the strong effects of geometry and size on the spin configurations of nanostructures are observed. In particular, a series of edged states occur in the circular disk-shaped lattices, and rich intricate saturated magnetization patterns appear in big lattices. It is suggested that the magnetic states can be manipulated by varying the perpendicular anisotropy, magneticfield, and geometry/size of the nanostructures. Furthermore, the stability (retention capacity) of the saturated magnetization states upon varying magneticfield is predicted, suggesting the potential applications of these saturated magnetization states in magneticfield-controlled data storages.

The voltage-induced magneticanisotropy change of an ultrathin ferrimagnetic FeGd alloy has been characterized using V|Fe90Gd10|MgO|Fe magnetic tunnel junctions. The bias-voltage dependence of the magnetoresistance measurement reveals the voltage-induced anisotropy change in the V|Fe90Gd10|MgO junction. The magneticanisotropyfield change (?Hk) in Fe90Gd10 is about twice that in Fe owing to the small net magnetization of the former. Therefore, employing ferrimagnetic materials is a promising option for voltage-controlled frequency-tunable spintronic devices.

Magnetic properties of Cr2O3 epitaxial clusters inserted in an Fe/MgO/Fe tunnel barrier are revealed by their tunnel magnetoresistance signature. The cluster assembly has been shown in a previous work to behave as a superparamagnet when a magneticfield was applied in the plane of the tunnel junction. We here demonstrate that an external large out-of plane electric field (in the order of 0.5 GV/m) favors in-plane magnetization orientation. This is due to an electric-field-induced magneticanisotropy along the normal to the plane, corresponding to large anisotropyfields reaching up to 2 T. The assembly of clusters is thus strictly speaking not superparamagnetic and its magnetization cannot be exactly described by a Langevin law. This is attributed either to a strain-induced enhanced magnetoelectric effect or to a voltage-induced change of the magneticanisotropy at interfaces with MgO.

The control of the magnetism of ultra-thin ferromagnetic layers using an electric field, rather than a current, has many potential technologically important applications. It is usually insisted that such control occurs via an electric field induced surface charge doping that modifies the magneticanisotropy. However, it remains the case that a number of key experiments cannot be understood within such a scenario. Much studied is the spin-splitting of the conduction electrons of non-magnetic metals or semi-conductors due to the Rashba spin-orbit coupling. This reflects a large surface electric field. For a magnet, this same splitting is modified by the exchange field resulting in a large magneticanisotropy energy via the Dzyaloshinskii-Moriya mechanism. This different, yet traditional, path to an electrically induced anisotropy energy can explain the electric field, thickness, and material dependence reported in many experiments. PMID:24531151

As an alternative to conventional magneticfield, the effective spin-orbit field in transition metals, derived from the Rashba field experienced by itinerant electrons confined in a spatial inversion asymmetric plane through the s-d exchange interaction, is proposed for the manipulation of magnetization. Magnetization switching in ferromagnetic thin films with perpendicular magnetocrystalline anisotropy can be achieved by current induced spin-orbit field, with small in-plane applied magneticfield. Spin-orbit field induced by current pulses as short as 10 ps can initiate ultrafast magnetization switching effectively, with experimentally achievable current densities. The whole switching process completes in about 100 ps.

We study how anisotropies of turbulent diffusion affect the evolution of large-scale magneticfields and the dynamo process on the Sun. The effect of anisotropy is calculated in a mean-field magnetohydrodynamics framework assuming that triple correlations provide relaxation to the turbulent electromotive force (so-called the 'minimal ?-approximation'). We examine two types of mean-field dynamo models: the well-known benchmark flux-transport model and a distributed-dynamo model with a subsurface rotational shear layer. For both models, we investigate effects of the double- and triple-cell meridional circulation, recently suggested by helioseismology and numerical simulations. To characterize the anisotropy effects, we introduce a parameter of anisotropy as a ratio of the radial and horizontal intensities of turbulent mixing. It is found that the anisotropy affects the distribution of magneticfields inside the convection zone. The concentration of the magnetic flux near the bottom and top boundaries of the convection zone is greater when the anisotropy is stronger. It is shown that the critical dynamo number and the dynamo period approach to constant values for large values of the anisotropy parameter. The anisotropy reduces the overlap of toroidal magneticfields generated in subsequent dynamo cycles, in the time-latitude 'butterfly' diagram. If we assume that sunspots are formed in the vicinity of the subsurface shear layer, then the distributed dynamo model with the anisotropic diffusivity satisfies the observational constraints from helioseismology and is consistent with the value of effective turbulent diffusion estimated from the dynamics of surface magneticfields.

Magnetoelectric coupling is studied using the electric field between the tip of a spin-polarized scanning tunneling microscope and a nanomagnet. Our experiments show that a negative (positive) electric field stabilizes (destabilizes) in-plane magnetization against thermal agitation, whereas it destabilizes (stabilizes) out-of-plane magnetization. We conclude that the electric field E induces a uniaxial anisotropy that favors in-plane magnetization for E <0 and out-of-plane magnetization for E>0. Our experiments demonstrate magnetic manipulation on the atomic scale without exploiting spin or charge currents.

The magnetocrystalline anisotropy of monoclinic chloritoid, a relatively common mineral in aluminum-rich, metapelitic rocks, has been determined for the first time by measuring the high-fieldanisotropy of magnetic susceptibility (HF-AMS), using two independent approaches, i.e., (a) directional magnetic hysteresis measurements and (b) torque magnetometry, on a collection of single crystals collected from different tectonometamorphic settings worldwide. Magnetic remanence experiments show that all specimens contain ferromagnetic (s.l.) impurities, being mainly magnetite. The determined HF-AMS ellipsoids have a highly oblate shape with the minimum susceptibility direction subparallel to the crystallographic c-axis of chloritoid. In the basal plane of chloritoid, though the HF-AMS can be considered isotropic. The degree of anisotropy is found to be 1.47, which is significantly higher than the anisotropy of most paramagnetic silicates and even well above the frequently used upper limit (i.e., 1.35) for the paramagnetic contribution to the AMS of siliciclastic rocks. The obtained values for the paramagnetic Curie temperature parallel (??) and perpendicular (??) to the basal plane indicate that this pronounced magnetocrystalline anisotropy is related to strong antiferromagnetic exchange interactions in the direction of the crystallographic c-axis (?? < 0) and rather weak ferromagnetic exchange interactions within the basal plane (?? > 0). As a consequence, chloritoid-bearing metapelites with a pronounced mineral alignment can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic, ferromagnetic (s.l.) minerals. The newly discovered magnetocrystalline anisotropy of chloritoid thus calls for a revised approach of magnetic fabric interpretations in chloritoid-bearing rocks.

It was suggested in recent papers that the crystal field parameters describing the rare-earth magneticanisotropy in metals should strongly depend on the orientation of the 4f shell, in contrast to a basic assumption of crystal field theory. By comparing the results of a perturbation approach with those from self-consistent calculations within the constrained local spin density approximation  including

The magneticanisotropyfield in thin films with in-plane uniaxial anisotropy can be deduced from the VSM magnetization curves measured in magneticfields of constant magnitudes. This offers a new possibility of applying rotational magnetization curves to determine the first- and second-order anisotropy constant in these films. In this paper we report a theoretical derivation of rotational magnetization curve in hexagonal crystal system with easy-plane anisotropy based on the principle of the minimum total energy. This model is applied to calculate and analyze the rotational magnetization process for magnetic spherical particles with hexagonal easy-plane anisotropy when rotating the external magneticfield in the basal plane. The theoretical calculations are consistent with Monte Carlo simulation results. It is found that to well reproduce experimental curves, the effect of coercive force on the magnetization reversal process should be fully considered when the intensity of the external field is much weaker than that of the anisotropyfield. Our research proves that the rotational magnetization curve from VSM measurement provides an effective access to analyze the in-plane anisotropy constant K 3 in hexagonal compounds, and the suitable experimental condition to measure K 3 is met when the ratio of the magnitude of the external field to that of the anisotropyfield is around 0.2.

In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg{sub 1?3}Nb{sub 2?3})O{sub 3}-PbTiO{sub 3} substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropyfield. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg1/3Nb2/3)O3-PbTiO3 substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropyfield. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

The anisotropy of magnetic susceptibility (AMS) is commonly used as a petrofabric tool. Whereas qualitative relationships between AMS and the petrofabric are well established, quantitative correlations are often ambiguous. For a quantitative interpretation of the paramagnetic component of a rock's AMS, the mineral source(s) of the paramagnetic fabric and their intrinsic contribution(s) should be understood. This requires knowledge about the intrinsic AMS of the rock-forming, paramagnetic minerals. For this study, the magnetocrystalline anisotropy of monoclinic chloritoid, a relatively common mineral in aluminium-rich, metapelitic rocks, has been determined for the first time by measuring the high-fieldanisotropy of magnetic susceptibility (HF-AMS) on a collection of single crystals, collected from different tectonometamorphic settings worldwide. Magnetic remanence experiments, i.e. (a) alternating-field (AF) demagnetization of a 1 T isothermal remanent magnetization (IRM) and a 200 mT anhysteretic remanent magnetization (ARM) and (b) low-temperature cycling of a room temperature saturation isothermal remanent magnetization (RT-SIRM), show that all specimens contain ferromagnetic (s.l.) impurities, being mainly magnetite. The determined HF-AMS ellipsoids have a highly oblate shape with the minimum susceptibility direction subparallel to the crystallographic c-axis of chloritoid. In the basal plane of chloritoid, however, the HF-AMS can be considered isotropic. The paramagnetic Curie temperature (?), which has been determined parallel and perpendicular to the basal plane, indicates a weak antiferromagnetic interaction in the direction of the crystallographic c-axis and a ferromagnetic interaction within the basal plane. The degree of anisotropy is found to be 1.48, which is significantly higher than the anisotropy of most paramagnetic silicates, i.e. the Fe-bearing phyllosilicates and the mafic silicates pyroxene, orthopyroxene, amphibole and olive, and even well above the frequently used upper limit (i.e. 1.35) for the paramagnetic contribution to AMS in siliciclastic rocks. As a consequence, chloritoid-bearing metapelites with a pronounced mineral alignment can have a higher degree of anisotropy than expected, without a significant contribution of strongly anisotropic, ferromagnetic (s.l.) minerals. The newly discovered magnetocrystalline anisotropy of chloritoid thus calls for a revised approach of magnetic fabric interpretations in chloritoid-bearing rocks.

Magnetoelectric effects in Fe\\/BaTiO3(001) heterostructures have been investigated via magneto-optical Kerr effect as a function of temperature. We find major modifications of magneticanisotropies and magnetic coercivity induced by the application of electric fields perpendicular to the interface. Changes in the coercive magneticfield, on the order of 100% at 250 K (in the orthorhombic phase of BaTiO3) and 40%

Supergranules in the quiet Sun are outlined by a web-like structure of enhanced magneticfield strength, the so-called magnetic network. We aim to map the magnetic network field around the average supergranule near disk center. We use observations of the line-of-sight component of the magneticfield from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The average supergranule is constructed by coaligning and averaging over 3000 individual supergranules. We determine the positions of the supergranules with an image segmentation algorithm that we apply to maps of the horizontal flow divergence measured using time-distance helioseismology. In the center of the average supergranule, the magnetic (intranetwork) field is weaker by about 2.2 Gauss than the background value (3.5 Gauss), whereas it is enhanced in the surrounding ring of horizontal inflows (by about 0.6 Gauss on average). We find that this network field is significantly stronger west (prograde) of the average supergranule than in the east (by about 0.3 Gauss). With time-distance helioseismology, we find a similar anisotropy. The observed anisotropy of the magneticfield adds to the mysterious dynamical properties of solar supergranulation.

Several cosmic-ray observatories have provided a high accuracy map of the sky at TeV--PeV energies. The data reveals an O(0.1%) deficit from north galactic directions that peaks at 10 TeV and then evolves with the energy, together with other anisotropies at smaller angular scales. Using Boltzmann's equation we derive expressions for the cosmic-ray flux that fit most of these features. The anisotropies depend on the local interstellar magneticfield B_{IS}, on the average galactic field B_{R} in our vicinity, and on the distribution of dominant cosmic-ray sources. We show that the initial dipole anisotropy along B_{IS} can be modulated by changes in the global cosmic ray wind, and that a variation in the dipole direction would imply a given radius of coherence for B_{IS}. We also show that small and medium-scale anisotropies may appear when the full-sky anisotropy finds a turbulence acting as a magnetic lens.

Electric-field-induced modification of magneticanisotropy is studied using tunnel magnetoresistance of the Co40Fe40B20/ MgO/ Co40Fe40B20 and Co40Fe40B20/ Hf (0.08?nm)/ MgO/ Co40Fe40B20 magnetic tunnel junctions. In both systems, the interfacial perpendicular magneticanisotropy is increased with increasing electron density at the MgO interface. A quantitative comparison between the two systems reveals that the change of magneticanisotropy energy with electric field is significantly enhanced in Co40Fe40B20/ Hf/ MgO/ Co40Fe40B20 compared to Co40Fe40B20/ MgO/ Co40Fe40B20. The sub-monolayer Hf insertion at the Co40Fe40B20/MgO interface turns out to be critical to the enhanced electric field control of the magneticanisotropy, indicating the interface sensitive nature of the effect.

We explore the magneticanisotropy of GaMnAs ferromagnetic semiconductor by Planar Hall Effect (PHE) measurements. Using low magnitude of applied magneticfield (i.e., when the magnitude H is smaller than both cubic Hc and uniaxial Hu anisotropyfield), we have observed various shapes of applied magneticfield direction dependence of Planar Hall Resistance (PHR). In particular, in two regions of temperature. At T < Tc/2, the "square-shape" signal and at T > Tc/2 the "zigzag-shape" signal of PHR. They reflect different magneticanisotropy and provide information about magnetization reversal process in GaMnAs ferromagnetic semiconductor. The theoretical model calculation of PHR based on the free energy density reproduces well the experimental data. We report also the temperature dependence of anisotropy constants and magnetization orientations. The transition of easy axis from biaxial to uniaxiale axes has been observed and confirmed by SQUID measurements. PMID:22905543

Hematite is one of the most important carriers of magnetic remanence in natural rocks. The magnetic properties of hematite bearing rocks have been intensively studied, particularly in the last decade, as instrumentation has become more sensitive, e.g., squid magnetometers and sophisticated vibrating sample magnetometers. The anisotropy of hematite and hematite-bearing rocks is more difficult to evaluate since its magnetic susceptibility is lower than other magnetic minerals such as magnetite. The magneticanisotropy of hematite, however, is often responsible for inclination shallowing of the remanence in hematite-bearing rocks. It is important to estimate this degree of flattening, so that remanence shallowing can be compensated when making paleoreconstructions of terrains. . The anisotropy of magnetic susceptibility has been measured on a collection of hematite single crystals in increasing low fields between 2 and 450 A/m in high fields up to 1.5 T using magnetic torque . Magnetic torque at 77K has also been measured on the largest crystals of the collection. The magnetic susceptibility ellipsoid and magnetic structure of the crystals have been studied with emphasis on the magnetic properties within the basal plane. Additional rock magnetic characterisation has been obtained from IRM acquisition curves, thermomagnetic curves and magnetic in order to constrain the composition of the samples. Results reveal that the magnetic susceptibility variation for hematite is out of the Rayleigh region for applied fields in commercial instruments. At high fields, the magnetic structure within the basal plane is a combination of biaxial and triaxial structures. The triaxial structure has different intensities probably due to different accumulations of stress within the crystal lattice as it is derived by torque measurements at low temperature.

The intergalactic magneticfield (IGMF) may leave an imprint on the angular anisotropy of the extragalactic gamma-ray background through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thereby inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that current Fermi data already seem to prefer nonnegligible IGMF values. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

We investigate the power spectrum of the distortion of the cosmic microwave background (CMB) due to the decay of the primordial magneticfields. It is known that there are two types of the CMB distortions, so-called ? and y types, and we find that the signal of the y-type distortion becomes larger than that of the ?-type one. We also discuss cross power spectra between the CMB distortions and the CMB temperature anisotropy, which are naturally generated due to the existence of the primordial magneticfields. We find that such cross power spectra have small amplitudes compared with the autopower spectra of the CMB distortions because of the Silk damping effect of the temperature anisotropy. We also investigate the possibility of detecting such a signal in the future CMB experiments, including not only absolutely calibrated experiments such as PIXIE but also relatively calibrated experiments such as LiteBIRD and CMBpol.

The anisotropy of the low-fieldmagnetic susceptibility (AMS), alternating-field-treated AMS (AF-AMS), and anisotropy of anhysteretic remanent magnetization (AARM) have been systematically examined for a sandwich sequence of loess/palaeosols crossing the upper loess unit L2 (Marine Oxygen Isotope Stage 6, MIS6) to the last interglacial maximum (palaeosol unit S1S3, MIS5e) from the Yuanbao section, northwestern China. Results show that a weak, but detectable, magnetic lineation is controlled by coarse-grained aeolian Fe3O4 (magnetite). Because the long axes of the coarse-grained magnetites are statistically parallel to the palaeowind directions, the declination of the maximum susceptibility principal axis of AMS can be used as an indicator of palaeowind direction. In contrast, fine-grained pedogenic magnetic particles are responsible for the magnetic foliation. We found that AF-AMS can indicate the domain state of the magnetic particles, which is consistent with Potter & Stephenson's earlier model. We also found that AF demagnetization can significantly alter the AMS. In conclusion, the angular dependence of AF-AMS can enhance the weak AMS fabrics.

though the Co:Fe ratio corresponded to the single phase fcc region of the binary Fe:Co phase diagram7B4 alloy. A mixture of nanocrystalline fcc and hcp phases surrounded by an amorphous matrix magneticanisotropy in binary alloys.5,6 A large transverse field-induced anisotropy is of interest

We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe3O4 nanoparticles (6nm) under the ON-OFF transient of an external dc magneticfield. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in the sample. We propose that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes.

We observe the anisotropy of the power spectral tensor of magneticfield fluctuations in the fast solar wind for the first time. In heliocentric RTN coordinates, the power in each element of the tensor has a unique dependence on the angle between the magneticfield and velocity of the solar wind ({theta}{sub B}) and the angle of the vector in the plane perpendicular to the velocity ({phi}{sub B}). We derive the geometrical effect of the high speed flow of the solar wind past the spacecraft on the power spectrum in the frame of the plasma P(k) to arrive at the observed power spectrum P(f, {theta}{sub B}, {phi}{sub B}) based on a scalar field description of turbulence theory. This allows us to predict the variation in the {phi}{sub B} direction and compare it to the data. We then transform the observations from RTN coordinates to magnetic-field-aligned coordinates. The observed reduced power spectral tensor matches the theoretical predictions we derive in both RTN and field-aligned coordinates, which means that the local magneticfield we calculate with wavelet envelope functions is an accurate representation of the physical axis of symmetry for the turbulence and implies that on average the turbulence is axisymmetric. We also show that we can separate the dominant toroidal component of the turbulence from the smaller but significant poloidal component and that these have different power anisotropy. We also conclude that the magnetic helicity is anisotropic and mostly two dimensional, arising from wavevectors largely confined to the plane perpendicular to B .

We study the dependence of the perpendicular magneticanisotropy on the underlayer material in magnetic tunnel junction. Using several different 4d and 5d metals we identify an optimal seed layer in terms of high anisotropy, low mixing, and high thermal stability. In such systems we investigate the tunability of the anisotropy by means of electric fields. Especially, by using W as the underlayer of the CoFeB/MgO/CoFeB trilayer we could obtain good thermal stability that allows for annealing in the temperatures up to 450 ?C , which results in high perpendicular anisotropy.

We examine a "two-component" model of the solar wind to see if any of the observed anisotropies of the fields can be explained in light of the need for various quantities, such as the magnetic minimum variance direction, to turn along with the Parker spiral. Previous results used a 3-D MHD spectral code to show that neither Q2D nor slab-wave components will turn their wave vectors in a turning Parker-like field, and that nonlinear interactions between the components are required to reproduce observations. In these new simulations we use higher resolution in both decaying and driven cases, and with and without a turning background field, to see what, if any, conditions lead to variance anisotropies similar to observations. We focus especially on the middle spectral range, and not the energy-containing scales, of the simulation for comparison with the solar wind. Preliminary results have shown that it is very difficult to produce the required variances with a turbulent cascade.

Multifunctionality of the magnetoelectric materials, simultaneous electric and magnetic orders, would offer a great opportunity in memory applications, in which switching the magnetization direction with an electric field is the main prerequisite. Ab initio calculations were carried out to reveal the importance of an epitaxial strain on magnetoelectric effects, possibly the spin reorientation of magnetization by ferroelectric polarization, in the interface between ferroelectric and ferromagnetic films. As a generic example, we show that the compressive strains larger than 1% that imposed to the in-plane lattice of SrTiO3 (001) underneath the Fe (001) overlayers result in a phase transition in magnetocrystalline anisotropy (MCA) from an in-plane to perpendicular magnetization with polarization reversal. A considerably large sensitivity of MCA with ferroelectric polarization is also found in the strained Fe/SrTiO3 (001), a factor of greater than those of well-studied multiferroic heterostructures. This switching of magnetization pertains to a competition of spin-orbit coupling states between t2 g bands, driven by the mutual mechanisms of the electrostatic screening with the spin-polarized carriers and the orbital hybridization at the interface. This work was supported by NSF Grant No. ERCTANMS- 1160504.

A torque-meter method of measuring the magneticanisotropy of rocks has been used in a study of a 1050-foot bore core from a Tasmanian dolerite sill. Each cylindrical specimen was suspended in a uniform field of 10.6 kilo-oersteds perpendicular to its axis, and the torque T exerted on it was measured at 10 ø intervals of the angle # between

Graded anisotropymagnetic materials possess a coercive field changing laterally with position. A simple fabrication procedure to produce such an anisotropy gradient in a polycrystalline Au/Co layer system without lateral thickness variation and with perpendicular magneticanisotropy, prototypical for a large variety of thin film systems, is shown. The procedure uses light-ion bombardment without the use of a mask. Magnetization reversal in this polycrystalline layer system takes place by unidirectional movement of a single domain wall only in regions with larger anisotropies and anisotropy gradients. In this anisotropy/anisotropy gradient regime, the domain wall is oriented perpendicular to the coercive field gradient, and it can be positioned along the gradient by an appropriate magneticfield pulse. For smaller anisotropies/anisotropy gradients, the natural anisotropy fluctuations of the polycrystalline layer system induce magnetization reversal dominated by domain nucleation. PACS 75.30.Gw; 75.70.Cn; 75.60.Ch PMID:25232291

We have experimentally studied micrometer-scale domain wall (DW) motion driven by a magneticfield and an electric current in a Co/Pt multilayer strip with perpendicular magneticanisotropy. The thermal activation energy for DW motion, along with its scaling with the driving field and current, has been extracted directly from the temperature dependence of the DW velocity. The injection of DC current resulted in an enhancement of the DW velocity independent of the current polarity, but produced no measurable change in the activation energy barrier. Through this analysis, the observed current-induced DW velocity enhancement can be entirely and unambiguously attributed to Joule heating. PMID:22173476

Corrections from the K 3 Dresselhaus term cubic in the wave vector to the energies of the ground and first excited Landau levels in III-V semiconductors have been analyzed. The calculated corrections together with the known corrections from the K 4 terms in the Hamiltonian of an electron provide a complete analytical description of the anisotropy of the conduction-band vertex of the III-V semiconductors in an ultraquantum magneticfield. The performed analysis of the experimental data on the splitting of the cyclotron resonance line in GaAs confirms the reality of the anisotropy mechanism under investigation.

In recent years neutrino oscillation experiments have showed that neutrinos have finite mass. One can determine the neutrino mass from neutrinoless double-beta decay experiments, but the exact mass of neutrinos is still unknown. However, we can also constrain the neutrino mass from a precise analysis of the CMB data, which constrains the mass to be smaller than 2 eV (2{sigma}) in a standard {lambda}CDM model [1]. In recent studies it has beddn shown that a primordial magneticfield (PMF) exists, and it makes important effects on the CMB anisotropies. In this work, we constrain the total neutrino mass from the CMB anisotropies with the PMF effect. We thus a obtained a smaller upper limit on the neutrino mass, i.e. <1.3 eV(2{sigma}). We will also discuss the dependence on the power law spectral index of the PMF and on the vector CMB anisotropies.

The static and dynamic magnetic properties of tetragonally distorted MnGa based alloys were investigated. Static properties are determined in magneticfields up to 6.5 T using SQUID magnetometry. For the pure Mn1.6Ga film, the saturation magnetisation is 0.36 MA m?1 and the coercivity is 0.29 T. Partial substitution of Mn by Co results in Mn2.6Co0.3Ga1.1. The saturation magnetisation of those films drops to 0.2 MA m?1 and the coercivity is increased to 1 T. The time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the high-frequency dynamics of MnGa. The ferromagnetic resonance frequency extrapolated to zero-field is found to be 125 GHz with a Gilbert damping, ?, of 0.019. The anisotropyfield is determined from both SQUID and TR-MOKE to be 4.5 T, corresponding to an effective anisotropy density of 0.81 MJ m?3. Given the large anisotropyfield of the Mn2.6Co0.3Ga1.1 film, pulsed magneticfields up to 60 T are used to determine the field strength required to saturate the film in the plane. For this, the extraordinary Hall effect was employed as a probe of the local magnetisation. By integrating the reconstructed in-plane magnetisation curve, the effective anisotropy energy density for Mn2.6Co0.3Ga1.1 is determined to be 1.23 MJ m?3.

FeCoB layers prepared on Ru underlayer possess a high saturation magnetization M{sub s} and a high in-plane magneticanisotropy filed H{sub k}. Effects of preparation conditions were investigated. Low Ar gas pressure condition and thicker film thickness were effective to attain distortion of FeCo crystallite. As the crystallinity of Ru underlayer became higher, higher H{sub k} was induced. The accumulation of anisotropic stress in the film caused by the oblique incidences of depositing atoms with high energy seems to be one of the important effects to attain high anisotropyfield. It was succeeded to prepare the Ru/FeCoB film with high H{sub k} of 500 Oe.

We present the magneticanisotropy of a 3-dimensional honeycomb iridate, where the large spin-orbit coupling of iridium provides the possibility for exotic magnetic ground states. A complete angular dependence of magnetic torque provides evidence for highly spin-anisotropic exchange interactions at low temperature. An extension of these measurements to high magneticfields shows that the magneticanisotropy switches sign at 50 T and becomes five times larger than the anisotropy at low fields. The anisotropy continues to increase up to the largest applied fields suggesting the presence of new magnetically ordered states.

The size dependent properties of monodomain ferromagnets are described. Following an introduction to the technical magnetics parameters used to describe bulk ferromagnets, the size dependence of these parameters is described. Bulk ferromagnetic materials are generally described as either hard or soft, depending on the value of their magnetocrystalline anisotropy. The role of anisotropy in monodomain ferromagnets is investigated through examination

We have investigated the effect of external magneticfield exercised during the fabrication of the Co and Co/Cu multilayer nanowires in anodic aluminum oxide (AAO) templates using pulse electrodeposition. It is found that the effect becomes significant when the pore size is small. Deterioration occurs in the magnetic properties for the Co nanowires studied, whereas a distinct enhancement in the magnetic properties for the Cu/Co multilayer nanowires is achieved by applying an external magneticfield during nanowire growth using the AAO template comprising pores of 50 nm diameter.

Textured MnBi crystals in a Bi matrix are fabricated by quenching at a high temperature (653 K) in a magneticfield of 10 T. Microstructure observations reveal that MnBi grains are aligned along their c-axis. Magnetization measurements show a pronounced magneticanisotropy in directions normal and parallel to the fabrication field resulting from the alignment. MnBi crystals display spin-disorder behaviors in ac magnetization, which may emerge due to the quenching processing.

It is shown that small-scale magneticfields present before recombination induce baryonic density inhomogeneities of appreciable magnitude. The presence of such inhomogeneities changes the ionization history of the Universe, which in turn decreases the angular scale of the Doppler peaks and increases Silk damping by photon diffusion. This unique signature could be used to (dis)prove the existence of primordial magneticfields of strength as small as B simeq 10-11 Gauss by cosmic microwave background observations.

Supergranules in the quiet Sun are outlined by a web-like structure of enhanced magneticfield strength, the so-called magnetic network. We aim to map the magnetic network field around the average supergranule near disk center. We use observations of the line-of-sight component of the magneticfield from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The average supergranule is constructed by coaligning and averaging over 3000 individual supergranules. We determine the positions of the supergranules with an image segmentation algorithm that we apply on maps of the horizontal flow divergence measured using time-distance helioseismology. In the center of the average supergranule the magnetic (intranetwork) field is weaker by about 2.2 Gauss than the background value (3.5 Gauss), whereas it is enhanced in the surrounding ring of horizontal inflows (by about 0.6 Gauss on average). We find that this network field is significantly stronger west (prograde) of the average sup...

In this article, we investigate the effect of electric-field on the perpendicular magneticanisotropy (PMA) and strain properties in nanoscaled CoFeB/MgO magnetic tunnel junction using tunnel magnetoresistance and piezoresponse force microscopy (PFM) measurements, respectively. We show that while the PMA change under electric-field is consistent with the previous reports, the PFM data show that the applied electric-field induces strain in a nanoscaled MgO. We demonstrate that the development of compressive and tensile strains corresponding to different polarities of applied electric-field. We discuss the interplay between the electric-field controlled PMA and strain properties. Our results may accelerate the development of magnetoelectrically controlled spintronic devices for low-power and high-density magnetic data storage applications.

We investigate electric-field effects on the effective magneticanisotropy energy density Keff and the Gilbert damping constant ? in Ta/CoFeB/MgO structures with CoFeB thickness t ranging from 1.4 to 1.8 nm by ferromagnetic resonance. The electric field-induced modulation ratio of the areal energy density Kefft does not depend on the CoFeB thickness, indicating that the electric-field effect on the magneticanisotropy originates from the modulation of CoFeB/MgO-interfacial magneticanisotropy. A clear electric-field modulation of ? is observed for the structure with t = 1.4 nm, and almost no modulation for the structures with t ? 1.5 nm.

Measurements of the magneticfield in our Galaxy are complex and usually difficult to interpret. A spiral regular field in the disk is favored by observations, however the number of field reversals is still under debate. Measurements of the parity of the field across the Galactic plane are also very difficult due to the presence of the disk field itself. In this work we demonstrate that cosmic ray protons in the energy range 1018 to 1019eV, if accelerated near the center of the Galaxy, are sensitive to the large scale structure of the Galactic MagneticField (GMF). In particular if the field is of even parity, and the spiral field is bi-symmetric (BSS), ultra high energy protons will predominantly come from the Southern Galactic hemisphere, and predominantly from the Northern Galactic hemisphere if the field is of even parity and axi-symmetric (ASS). There is no sensitivity to the BSS or ASS configurations if the field is of odd parity.

Magnetic clustering, thermal stability, and recording performance on perpendicular media with multilayered magneticanisotropyfield (Hk)-gradient CoPtCr-oxide/Cap layers with various Ru-oxide layer thicknesses (tRu-oxide) on top of Ru/NiW layers are investigated. With increasing tRu-oxide from 0 to 1.3 nm, Hc and Hs are enhanced but Hn is reduced. Magnetic correlation length (Dn) extracted from a set of major and minor loops significantly decreases but intrinsic switching field distribution remains unaffected. A short-time switching field (Ho) proportional to Hk increases linearly while KuV/kT remains unchanged. Similar KuV/kT is explained by compensation of the reduced Dn with the enhanced Ku induced by a thin Ru-oxide. However, thermal decay rate degrades from 0.06 to 0.32%/decade, which correlates well with Hn. Similar values of initial minor loop slopes indicate no change in magnetic switching behavior. A 1 nm-thick Ru-oxide layer as a well-defined granular template significantly improves recording performance: narrower MCW at 10 T by 8 nm and higher SNR at 2 T by 1.4 dB are observed even at lower OW by 8 dB compared to the media without Ru-oxide. All the recording parameters as a function of Dn correlate well.

Recent results from the Pierre Auger Observatory (PAO) indicate that the composition of ultra-high-energy cosmic rays (UHECRs) with energies above 1019 eV may be dominated by heavy nuclei. An important question is whether the distribution of arrival directions for such UHECR nuclei can exhibit observable anisotropy or positional correlations with their astrophysical source objects despite the expected strong deflections by intervening magneticfields. For this purpose, we have simulated the propagation of UHECR nuclei including models for both the extragalactic magneticfield (EGMF) and the Galactic magneticfield (GMF). We find that the GMF is particularly crucial for suppressing the anisotropy as well as source correlations. Assuming that only iron nuclei are injected steadily from sources with equal luminosity and spatially distributed according to the observed large scale structure in the local Universe, at the number of events published by the PAO so far (69 events above 5.5 × 1019 eV), the arrival distribution of UHECRs would be consistent with no auto-correlation at 95% confidence if the mean number density of UHECR sources ns ? 10-6 Mpc-3, and consistent with no cross-correlation with sources within 95% errors for ns ? 10-5 Mpc-3. On the other hand, with 1000 events above 5.5 × 1019 eV in the whole sky, next generation experiments can reveal auto-correlation with more than 99% probability even for ns ? 10-3 Mpc-3, and cross-correlation with sources with more than 99% probability for ns ? 10-4 Mpc-3. In addition, we find that the contribution of Centaurus A is required to reproduce the currently observed UHECR excess in the Centaurus region. Secondary protons generated by photodisintegration of primary heavy nuclei during propagation play a crucial role in all cases, and the resulting anisotropy at small angular scales should provide a strong hint of the source location if the maximum energies of the heavy nuclei are sufficiently high.

An amorphous Co{sub 68}Fe{sub 24}Zr{sub 8}(3 nm)/Al{sub 70}Zr{sub 30}(3 nm)/Co{sub 68}Fe{sub 24}Zr{sub 8}(3 nm) trilayer system has been investigated using in-plane and out-of-plane angular dependent ferromagnetic resonance at different frequencies. The in-plane magneticanisotropy is uniaxial, retaining its value of (2.9 {+-} 0.1) x 10{sup 3} J/m{sup 3} for each magnetic layer, whereas its direction was tailored independently in an arbitrary manner by applying an external magneticfield during the film deposition. The perpendicular anisotropy constant, supposed to reflect the interface quality, is nearly identical for both layers. Furthermore, the magnetic layers act independently upon each other due to the absence of interlayer coupling.

Laboratory observation of rotation of the polarization axis ({theta}{sub c{approx}}20 deg. - 40 deg. with respect to vacuum) of a penetrating electromagnetic wave through a bounded supercritical plasma (plasma frequency {omega}{sub p}>wave frequency {omega}), confined in a multicusp magneticfield is reported. Birefringence of the radial and polar wave electric field components (E{sub r} and E{sub {theta}}) has been identified as the cause for the rotation, similar to a magneto-optic medium, however, with distinct differences owing to the presence of wave induced resonances. Numerical simulation results obtained by solving the Maxwell's equations by incorporating the plasma and magnetostatic field inhomogeneities within a conducting boundary shows a reasonable agreement with the experimental results.

Hitperm-type rapidly quenched ribbons were submitted to field annealing, both longitudinal field (LF) and transversal field (TF) to the axis of the ribbon. LF annealing yields a reduction of the magneticanisotropy and results can be explained in the frame of random anisotropy model. A coercivity of 3 A/m is obtained for Fe39Co39Nb6B15Cu1 alloy. The addition of Cu to these Nb-containing Hitperm-type alloys is a key factor to refine the microstructure in order to reach this very low coercivity value. TF annealing produces samples with sheared hysteresis loops suitable for sensor and high frequency applications.

L1(sub 0)-ordered FePd epitaxial thin films were prepared using dc magnetron sputter deposition on MgO (001) substrates. The films were grown with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magneticanisotropy, and magnetic domain structure. The experimentally measured domain size/period and magneticanisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

By the infinite time-evolving block decimation (iTEBD) technique, the magnetization process and the quantum phase transitions (QPTs) in the spin-1 XXZ model with single-ion anisotropy under external field are investigated. It is found that, all the phases will be destroyed by a sufficient strong magneticfield. Before they come into the ferromagnetic (fully polarized) phase, some interesting intermediate phases are induced. A pseudo order Oixy=?{

The conventional rules, derived from empirical and theoretical considerations, for the interpretation of anisotropy of magnetic susceptibility (AMS) in terms of microstructure and deformation are subject to numerous exceptions as a result of particular rock magnetic effects. Unusual relationships between structural and magnetic axes (so-called inverse or intermediate magnetic fabrics) can occur because of the presence of certain magnetic minerals, either single domain magnetite or various paramagnetic minerals. When more than one mineral is responsible for magnetic susceptibility, various problems appear, in particular the impossibility of using anisotropy to make quantitative inferences on the intensity of the preferred orientation and consequently on strain. In ferromagnetic grains, AMS may also be influenced by the magnetic memory of the grains (including natural remanence). The effect of alternating field or thermal demagnetization on AMS is briefly discussed. As discussed in this article, various rock magnetic techniques, specific to AMS interpretation, have to be developed for a better assessment of the geological significance of AMS data. These techniques mainly rely on measurements of susceptibility versus magneticfield and temperature, together with anisotropy of remanence. 93 refs., 11 figs., 1 tab.

A spin-1 transverse Ising model with longitudinal crystal field in a longitudinal magneticfield is examined by introducing an effective field approximation (IEFT) which includes the correlations between different spins that emerge when expanding the identities. The effects of the crystal field as well as the transverse and longitudinal magneticfields on the thermal and magnetic properties of the spin

Nucleonic intensity data from the north and south polar stations Thule and McMurdo are analyzed to determine the nature of periodicities in the north-south asymmetry of relativistic galactic cosmic rays. The 24-hour average intensity differences of individual days range from 0 to +- 1.5%, and the most prominent time variation is recurrence tendency with a period consistent with the 27-day solar rotation period. A recently developed procedure for evaluating the statistical significance of quasipersistent data has been utilized to establish the reality of the 27-day signal disclosed by superposed epoch analysis of the north-south asymmetry data. Analyses of various components of the interplanetary magneticfield reveal that the IMF component B-bar/sub ..mu../ (parallel to the nominal garden hose direction) also displays a 27-day variation with maximum amplitude. Furthermore, a significant relationship between B-bar/sub ..mu../ and the north-south asymmetry is established by Chree analysis. On the basis of this relationship, it is suggested that the 27-day variation in the north-south asymmetry arises from the B-bar/sub ..mu../ x del-bar(n) drift, where del-bar(n) represents the radial gradient of cosmic rays.

In a previous paper [A. Mori, T. Kaito, H. Furukawa, Mater. Lett. 62 (2008) 3459-3461], we carried out birefringence measurements of Pb(II)-doped silica hydrogels prepared in a magneticfield (B). For a 5T sample, we observed a negative birefringence with the optic axis along B. At that time, providing a positive intrinsic birefringence of silica, we speculated that in the birefringent gels the gel network extended perpendicular to B. The purpose of this paper is to reconsider this speculation on the basis of previous and recent results [T. Kaito, S.-i. Yanagiya, A. Mori, M. Kurumada, C. Kaito, T. Inoue, J. Cryst. Growth 289 (2006) 275-277; T. Kaito, A. Mori, C. Kaito, J. Chem. Chem. Eng., 9 (2015) 61-66]. In the former, the silica gels were used as a medium of a crystal growth of PbBr2 and aligned arrays of crystallites with long axis parallel to B were obtained. In the latter, Pb(II) nanocrystallites were formed in silica xerogels by electron irradiation. Both of the short axis of PbBr2 crystallites and the...

Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magneticanisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.

Although the crystal-field ground state in the paramagnetic phase of CeP is ?7, part of cerium ions take a ?8-like state in magnetically ordered phases and regular arrangements of the ?7 and ?8-like moments constitute magnetic structures. We have performed transverse magnetoresistance measurements up to 32 T for selected field directions and have determined phase boundaries related to the appearance of the ?8-like state for each field direction. The result reveals the extreme uniaxial anisotropy that the ?8-like moment is strongly bound to the [001] axis. We have also determined the field-orientation dependence of phase transitions connected with the rearrangement of the ?7 moment via ac susceptibility measurements. The analysis of the angular dependence indicates that the ?7 moment prefers the [001] direction only weakly probably due to the exchange field from neighboring ?8 moments. The resistivity exhibits a sharp decrease on the appearance of the ?8-like state. Besides, Hall effect measurements up to 26 T show a concomitant reduction of the magnitude of the Hall coefficient, and suggest the presence of the anomalous Hall effect in the magnetically ordered phases. These indicate that the appearance of the ?8-like state is accompanied by a drastic change of the electronic structure.

Some igneous rocks are magnetized in a direction opposite to that expected, if they had been cooled in the earth's magneticfield. These rocks are said to have a reverse thermo-remanent magnetization (reverse TRM). Uyeda has shown that the reverse TRM of the Haruna deposit in Japan is due to an ilmenite-hematite solid solution and has synthesized a solid solution

Quantitative experimental results have been obtained in support of a previously developed theory which represents the deformation of the critical curves of multilayered magnetic thin films in terms of effective multiaxial anisotropies. The effective biaxial anisotropyfield has been experimentally observed to be proportional to the square of film thickness in the case of thinner films, as expected from the

We study the effects of external magneticfield on the properties of an ordered Heisenberg antiferromagnet with the Dzyaloshinskii-Moriya (DM) interaction. Using the spin-wave theory quantum correction to the energy, on-site magnetization, and uniform magnetization are calculated as a function of the field H and the DM anisotropy constant D . It is shown that the spin-wave excitations exhibit an unusual field evolution of the gaps. This leads to various nonanalytic dependencies of the quantum corrections on H and D . It is also demonstrated that, quite generally, the DM interaction suppresses quantum fluctuations, thus driving the system to a more classical ground state. Most of the discussion is devoted to the spin- S , two-dimensional square lattice antiferromagnet, whose S=(1)/(2) case is closely realized in K2V3O8 where at H=0 the DM anisotropy is hidden by the easy-axis anisotropy but is revealed in a finite field. The theoretical results for the field dependence of the spin-excitation gaps in this material are presented and the implications for other systems are discussed.

Galactic hemisphere if the field is of even parity and axi-symmetric (ASS). There is no sensitivity to the BSS or ASS configurations if the field is of odd parity. 1. Introduction The position of the Solar of the spiral field, axi-symmetric (ASS) or bi-symmetric (BSS) [2, 9]. The number of field reversals is still

Thin film heterostructures of transition metal ferromagnets (FM) and polymer ferroelectrics (FE) are investigated to look for changes in the magneticanisotropy of the FM layer that occur on switching the FE polarization (with an ensuing change in the electric field direction).[1] Samples of [Glass/ Pd (50 nm)/Co wedge (0.9-2.6nm)/ferroelectric P(VDF-TrFE) (53 nm)/Al (30nm)] are deposited via sputtering or evaporation for the metallic layers and via Langmuir-Schaefer deposition for the polymer ferroelectric. [2] Magnetic and FE properties have been characterized using the Magneto-Optical Kerr Effect (MOKE) and the pyroelectric effect. Polar and longitudinal MOKE loops are measured across the Co wedge for both positive and negative FE polarization and the difference in the two MOKE loops is ascribed to the changes in the magneticanisotropy of the FM layer. [3] These changes are most apparent in the region where the Co undergoes a transition from in-plane to out-of-plane anisotropy. This research is supported by the NSF MRSEC through Grant No. DMR- 0820521 1. Chun-Gang Duan et al, Appl. Phys. Lett. 92, 122905 (2008) 2. A. V. Bune, et al, Nature (London) 391, 874 (1998) 3. P. F. Carcia, J.Appl. Phys. 63, 5066 (1988)

We grow perpendicular L10-FePt films epitaxially on (001)[Pb(Mg1/3Nb2/3)]0.7-(PbTiO3)0.3 ferroelectric substrates. Due to the magnetostriction effect, the out-of-plane coercivity (Hc?) of the L10-FePt varies with applied electric fields, showing an asymmetric butterfly-like loop. The Hc? at the zero-electric-field state (Hc?,0) shows a nonvolatile change, depending on the direction of the poling electric field. The magnitude of nonvolatile magneticanisotropy change, induced by the ferroelectric field effect, can be comparable to the anisotropy change induced by pure electric fields. The nonvolatile magneticanisotropy change is inversely proportional to the FePt thickness and can be eliminated by inserting a metallic intermediate layer.

properties in spintronic devices. The most commonly investigated material as a magnetic semiconductor is GaAsPHYSICAL REVIEW B 88, 205203 (2013) Magneticanisotropy of single Mn acceptors in GaAs Photonics and Semiconductor Nanophysics, Department of Applied Physics, Eindhoven University of Technology

A systematic study of the magnetic properties and anisotropy in magnetic thin films as well as superlattices is presented in this thesis. The main objective is to investigate by means of the Green function technique the order-disorder phase transition and reorientation transition in a non-perturbative microscopic theory valid in the whole temperature range of interest. We consider the magnetic systems that may consist of an arbitrary number of layers with any spin. We start with a discussion of general properties and origins of anisotropies of the magnetic systems, and a list of questions that we are trying to answer. A comparison between different theoretical approaches follows. The Green function method is used to derive analytical expressions for various anisotropies. The energy spectrum and the spontaneous magnetization are obtained as well. Based on these results, the transition temperature and the Curie temperature are calculated as functions of the Fe film thickness. It is shown that the condition for the reorientation transition is equivalent to that for the zero energy gap at the bottom of the spin-wave spectrum. Special features under the influence of normal external field, anisotropic exchange couplings and next-nearest-neighbor couplings on the magnetization reorientation of magnetic thin films are then investigated in detail. It is demonstrated that the nature of perpendicular remanent (PR) depends primarily on the surface anisotropy and film thickness. The magnetic properties of Tb/Fe superlattices are also studied. It shows ferrimagnetic properties and normal uniaxial anisotropy. An approximation is proposed to treat magnetic Ni films of arbitrary thickness and arbitrary lattice structure for general spin. It is a much simpler way of calculation, in which one does not have to solve the determinant equation, especially the one with off-diagonal elements. The temperature and thickness dependence of various anisotropies are then investigated. There exists a PR magnetization for a medium size of film thickness. Finally, a summary and conclusion are given and some general perspectives of the field are discussed.

The effects of partial substitution of Co on magnetocrystalline anisotropy and magnetic-field-induced strain (MFIS) in NiFeGa alloys have been investigated. To obtain a single-variant state in the martensite phase, uniaxial compressive stresses were applied to the single-crystalline specimen. The Curie temperature TC is increased up to 405K by a partial substitution of 6at% Co. The single-variant martensite phase in the

Magneticanisotropy is investigated systematically for the textured MnBi crystal. The magneticanisotropy exists in magnetization behaviors, hysteresis loops, and remnant magnetization. An abnormal coercivity field Hc is found in the textured MnBi: Hc perpendicular to the c-axis is larger than that parallel to the c-axis. The mechanism of anisotropy is discussed based on magnetocrystalline anisotropy in MnBi. The behavior

Magnetic nanoparticles have applications to a variety devices ranging from high density magnetic data storage to targeted drug delivery. The suitability of specific magnetic nanoparticles for a particular application is mainly determined by their magneticanisotropy energy. Magnetic nanoparticles with large magneticanisotropy energy are particularly useful for high density data storage while the magnetic nanoparticles with small magneticanisotropy

A study has been carried out of the magnetization of a layered system consisting of two exchange-coupled easy-axis ferromagnetic\\u000a layers separated by a nonmagnetic spacer and having mutually perpendicular anisotropy axes. It is shown that the magnetization\\u000a of such a system can undergo stepwise decrease with increasing magneticfield. The field dependence of the magnetization has\\u000a a bifurcation point. The

Ferromagnetic nanocomposites, or ''exchange spring'' magnets, possess a nanoscaled microstructure that allows intergrain magnetic exchange forces to couple the constituent grains and alter the system's effective magneticanisotropies. While the effects of the anisotropy alterations are clearly seen in macroscopic magnetic measurement, it is extremely difficult to determine the detailed effects of the system's exchange coupling, such as the interphase exchange length, the inherent domain wall widths or the effective anisotropies of the system. Clarification of these materials parameters may be obtained from the ''micromagnetic'' phenomenological model, where the assumption of magnetic reversal initiating in the magnetically-soft regions of the exchange-spring maqet is explicitly included. This approach differs from that typically applied by other researchers and allows a quantitative estimate of the effective anisotropies of an exchange spring system. Hysteresis loops measured on well-characterized nanocomposite alloys based on the composition Nd{sub 2}Fe{sub 14}B + {alpha}-Fe at temperatures above the spin reorientation temperature were analyzed within the framework of the micromagnetic phenomenological model. Preliminary results indicate that the effective anisotropy constant in the material is intermediate to that of bulk {alpha}-Fe and bulk Nd{sub 2}Fe{sub 14}B and increases with decreasing temperature. These results strongly support the idea that magnetic reversal in nanocomposite systems initiates in the lower-anisotropy regions of the system, and that the soft-phase regions become exchange-hardened by virtue of their proximity to the magnetically-hard regions.

We consider the Casimir interaction between a ferromagnetic and a nonmagnetic mirror and show how the Casimir effect gives rise to a magneticanisotropy in the ferromagnetic layer. The anisotropy is out of plane if the nonmagnetic plate is optically isotropic. If the nonmagnetic plate shows a uniaxial optical anisotropy (with optical axis in the plate plane), we find an in-plane magneticanisotropy. In both cases, the energetically most favorable magnetization orientation is given by the competition between polar, longitudinal, and transverse contributions to the magneto-optical Kerr effect and will therefore depend on the interplate distance. Numerical results will be presented for a magnetic plate made out of Fe and nonmagnetic plates of Au (optically isotropic), quartz, calcite, and barium titanate (all uniaxially birefringent).

To understand the distribution of the in-plane magneticanisotropy under a dc electric field, FeCo films deposited onto Pb(Mg1/3Nb2/3)O3-PbTiO3 (011)-orientated substrates by RF-magnetron sputtering were investigated. Vibrating sample magnetometer was performed and the occurrence of switching was demonstrated of the magnetization easy axis in FeCo films upon applying solely a dc electric field. A theoretical calculation was performed to provide a simplified account of the magnetoelastic contribution to the magneticanisotropy. Quantification of the angular distribution of the magneticanisotropyfield under various electric fields was obtained, which can contribute to realizing low-loss electric-field-turning devices.

Using first-principles calculations, we predict that the magneticanisotropy energy of Co-doped TiO2 sensitively depends on carrier accumulation. This magnetoelectric phenomenon provides a potential route to a direct manipulation of the magnetization direction in diluted magnetic semiconductor by external electric-fields. We calculate the band structures and reveal the origin of the carrier-dependent magneticanisotropy energy in k-space. It is shown that the carrier accumulation shifts the Fermi energy, and consequently, regulates the competing contributions to the magneticanisotropy energy. The calculations provide an insight to understanding this magnetoelectric phenomenon, and a straightforward way to search prospective materials for electrically controllable spin direction of carriers. PMID:25510846

By a magnetic-field-inducing technique, Bi-Mn alloys were fabricated with the textured structure and anisotropic characteristics. Magnetic properties of MnBi compound aligned in alloys with 6 wt % Mn have been investigated systematically. The saturation magnetization Ms decreases with the increase of temperature. At temperatures below 150K , the coercive field Hc decreases with the increase of temperature, while the coercive field Hc increases with temperature above 150K . In the range of temperature from 150 to 300K , the remanent magnetization Mr and the Mr/Ms increase with the temperature, while below 150K , the Mr and the Mr/Ms reach a constant value of nearly zero. The magnetic moments rotated from being parallel to the c axis toward the basal plane for MnBi (the low-temperature phase) at about 90K . Most of all, under a dc magneticfield applied parallel to the c axis, the transition temperature of the spin reorientation decreases with the increase of magneticfield, and even decreases 30K under 5T . The mechanism of the spin-reorientation transition and the change of its transition temperature are discussed and explained by phenomenological theory.

Magneticanisotropy plays a key role in the magnetic stability and spin-related quantum phenomena of surface adatoms. It manifests as angular variations of the atom's magnetic properties. We measure the spin excitations of individual Fe atoms on a copper nitride surface with inelastic electron tunneling spectroscopy. Using a three-axis vector magnet we rotate the magneticfield and map out the resulting variations of the spin excitations. We quantitatively determine the three-dimensional distribution of the magneticanisotropy of single Fe atoms by fitting the spin excitation spectra with a spin Hamiltonian. This experiment demonstrates the feasibility of fully mapping the vector magnetic properties of individual spins and characterizing complex three-dimensional magnetic systems. PMID:25664924

Magnetoferritin molecules with an average inorganic core diameter of 5.7±1.6 nm and polycrystalline internal structure were investigated by a combination of transmission electron microscopy, magnetic susceptibility, magnetization, and electron magnetic resonance (EMR) experiments. The temperature and frequency dependence of the magnetic susceptibility allowed for the determination of the magneticanisotropy on an experimental time scale which spans from seconds to nanoseconds. In addition, angle-dependent EMR experiments were carried out for the determination of the nanoparticle symmetry and internal magneticfield. Due to the large surface to volume ratio, the nanoparticles show larger and uniaxial rather than cubic magneticanisotropies compared to bulk maghemite and magnetite.

We investigate the high-frequency response of magnetization dynamics through magnetoimpedance (MI) effect in Permalloy-based multilayered thin films produced with two different non-magnetic metallic spacers: Cu and Ag. Due to the nature of the spacer materials, we are able to play with magnetic properties and to study both systems with weak/strong magneticanisotropy. We verify very rich features in the magnetoimpedance behavior and high magnetoimpedance ratios, with values above 200%. We compare the MI results obtained in multilayered thin films with distinct spacers and number of bilayers, and discuss them in terms of the different mechanisms that govern the MI changes observed at distinct frequency ranges, intensity of the magneticanisotropy, alignment between dc magneticfield and anisotropy direction. Besides, by considering a theoretical approach that takes into account two single models together and calculate the transverse magnetic permeability and the MI effect, we support our interpretation via numerical calculations modeling the effect of weak/strong magneticanisotropy on the MI response. Thus, we confirm that these features are very important for the use of multilayered films in sensor applications and, both the frequency and field response can be tailored to fulfill the requirements of a given device.

The conventional rules, derived from empirical and theoretical considerations, for the interpretation of anisotropy of magnetic susceptibility (AMS) in terms of microstructure and deformation are subject to numerous exceptions as a result of particular rock magnetic effects. Unusual relationships between structural and magnetic axes (so-called inverse or intermediate magnetic fabrics) can occur because of the presence of certain magnetic minerals,

Magneticanisotropy measurements are becoming increasingly common to many studies within the different disciplines of geology, involving sedimentary, igneous and metamorphic rocks. A plethora of techniques exists for measuring magneticanisotropy of rocks. Some are rapid and non-destructive while others are more labor-intensive or may result in alteration of the magnetic minerals. All, however, have the potential of revealing a wealth of information when measured and interpreted correctly. In broad terms, anisotropy techniques subdivide into measurements of susceptibility, remanence and torque; here we consider the first two of these. Anisotropy of magnetic susceptibility (AMS) is by far the most utilized, and measures composite fabrics. Magnetic susceptibilities in high fields and low temperatures, however, are being increasingly used to isolate the paramagnetic contribution to the fabrics. When distinguishing between fabrics carried by different ferromagnetic phases, or to separate these from the diamagnetic and paramagnetic contributions to the fabric, then remanence anisotropy techniques become necessary. Anisotropies of thermal remanence (ATRMs), of anhysteretic remanence (AARM) and of isothermal remanence (AIRM) are the most common examples. Remanence anisotropy may be measured over the full spectrum of magnetic coercivities or over a targeted range (e.g. partial or ApARM). Moreover, anisotropies may be calculated using only the resolved field-parallel component of the vector, in which case a minimum of six different orientations is necessary to obtain a complete symmetric tensor, or using the three components (full vector) of the measured magnetic vectors (e.g. AvARM), in which case three orthogonal applied magnetizations are the minimum requirement. In this study we utilize a variety of magnetic remanence room temperature techniques to measure remanence anisotropy of selected coarse and finer grained gneiss-granulitic specimens with well-pronounced fabrics. Results are compared to room temperature AMS and are interpreted in terms of the applicability of instrumentation/technique to specific rock-magnetic properties.

The perturbation to the ligand field around the lanthanide ion may significantly contribute to the magnetic dynamics of single molecule magnets. This can be demonstrated by two typical Dy4 cluster-based single molecular magnets (SMMs), [Dy4X2(?3-OH)2(?-OH)2(2,2-bpt)4(H2O)4]X2·2H2O·4EtOH (X = Cl and Br for and , respectively), which were constructed by using 3,5-bis(pyridin-2-yl)-1,2,4-triazole (2,2-bptH) as the polynuclear-chelating ligand. Alternating-current (ac) magnetic susceptibility measurements show that the energy barriers in complexes and were immensely enhanced by comparing with our previous work due to the optimization of the ligand field around Dy(III) ions. Remarkably, their high thermal active barriers at 190 K () and 197 K () under a zero applied external dc magneticfield are also among the highest within the reported tetranuclear lanthanide-based SMMs. PMID:25837027

, the critical temperatures, the coercive fields and the magnetocrystalline anisotropy constants as a function of magnetocrystalline origin, and directly reflects the anisotropy of the valence band (VB) through the spin1 Evolution of the magneticanisotropy with carrier density in hydrogenated (Ga,Mn)As L. Thevenard

Saturation magnetization as well as anisotropyfield have been measured versus temperature and composition for the alloy Co 1- xCr x in the range 0 ? x ? 0.25 from 77 to 1000 K. Curie and phase transition temperatures of the alloy have been determined in the above composition range using thermomagnetic analysis.

Recently, voltage controlled magneticanisotropy (VCMA) in 3d transitional ferromagnets (FM) has attracted a great deal of attentions. VCMA has traditionally been explored in multiferroic materials and diluted magnetic semiconductors, but not in metals because of the anticipated negligible effects since the electric field would be screened within 1-2 Å at the metal surface. However, a voltage may exert marked effects if the magnetic properties of ultrathin films are dominated by interfacial magneticanisotropy. Here we demonstrate a large VCMA effect in perpendicular MgO magnetic tunnel junctions (p-MTJs) with very thin CoFeB layers. The p-MTJs have the key structure of Co40Fe40B20(1.2-1.3nm)/MgO(1.2-2nm)/Co40Fe40B20(1.6nm) exhibiting at room temperature tunneling magnetoresistance in excess of 100%. The perpendicular magneticanisotropy (PMA) in this system is believed to be stabilized by hybridization between the out-of-plane 3d orbitals of the FM and oxygen 2p orbitals. We show that both the magnitude and the direction of the electric field can systematically alter the PMA of the thin CoFeB layers interfaced with the MgO barrier. Furthermore, under a given electric field, the two CoFeB layers on either side of the MgO barrier respond in the opposite manner as expected. By exploiting the combined effect of spin transfer torque and VCMA in CoFeB/MgO/CoFeB nanopillars, we have accomplished voltage controlled spintronic devices, where the MTJ can be manipulated by a unipolar switching process using consecutive negative voltages less than 1.5 V in magnitude. In this manner, voltage can access the high resistance or the low resistance state of an MTJ with very small current densities. Wang, W.-G., Li, M., Hageman, S. & Chien, C. L. Electric-field-assisted switching in magnetic tunnel junctions. Nature Materials 11, 64 (2012). Recently, voltage controlled magneticanisotropy (VCMA) in 3d transitional ferromagnets (FM) has attracted a great deal of attentions. VCMA has traditionally been explored in multiferroic materials and diluted magnetic semiconductors, but not in metals because of the anticipated negligible effects since the electric field would be screened within 1-2 Å at the metal surface. However, a voltage may exert marked effects if the magnetic properties of ultrathin films are dominated by interfacial magneticanisotropy. Here we demonstrate a large VCMA effect in perpendicular MgO magnetic tunnel junctions (p-MTJs) with very thin CoFeB layers. The p-MTJs have the key structure of Co40Fe40B20(1.2-1.3nm)/MgO(1.2-2nm)/Co40Fe40B20(1.6nm) exhibiting at room temperature tunneling magnetoresistance in excess of 100%. The perpendicular magneticanisotropy (PMA) in this system is believed to be stabilized by hybridization between the out-of-plane 3d orbitals of the FM and oxygen 2p orbitals. We show that both the magnitude and the direction of the electric field can systematically alter the PMA of the thin CoFeB layers interfaced with the MgO barrier. Furthermore, under a given electric field, the two CoFeB layers on either side of the MgO barrier respond in the opposite manner as expected. By exploiting the combined effect of spin transfer torque and VCMA in CoFeB/MgO/CoFeB nanopillars, we have accomplished voltage controlled spintronic devices, where the MTJ can be manipulated by a unipolar switching process using consecutive negative voltages less than 1.5 V in magnitude. In this manner, voltage can access the high resistance or the low resistance state of an MTJ with very small current densities. Wang, W.-G., Li, M., Hageman, S. & Chien, C. L. Electric-field-assisted switching in magnetic tunnel junctions. Nature Materials 11, 64 (2012). This work is done in collaboration with Mingen Li, Stephen Hageman and C. L. Chien. Research is supported by the NSF grant DMR 05-20491.

Students visualize the magneticfield of a strong permanent magnet using a compass. The lesson begins with an analogy to the effect of the Earth's magneticfield on a compass. Students see the connection that the compass simply responds to the Earth's magneticfield since it is the closest, strongest field, and thus the compass responds to the field of the permanent magnets, allowing them the ability to map the field of that magnet in the activity. This information will be important in designing a solution to the grand challenge in activity 4 of the unit.

A novel bi-directional magnetic microactuator using electroplated permanent magnet arrays has been fabricated and tested in this work. To realize the microactuator, a new electroplating technique has been developed to improve vertical magneticanisotropy in CoNiMnP-based permanent magnet arrays. By applying magneticfield during electroplating, vertical coercivity and remanence have been increased up to 1100 Oe and 1900 G. After

Low-temperature nuclear orientation was applied to study hyperfine interactions of 142Pr, 147Nd and 143,144Pm nuclei in Pr0.5Nd0.5Ni single crystal. Angular distributions, temperature dependence and external magneticfield effects on the ?-ray anisotropy are presented. A Nd-Pm exchange interaction seems to dominate the magnetic properties of Pm ions in this system.

Heisenberg interaction. Molecules with even larger gaps abound in the chemistry of molecular magnets, where of anisotropy by analysing the trans- port properties of a high-spin quantum dot embedded between two. The high-spin quantum dot, described by Hdot = ^n + U ^n^n + K^s Â· ^Simp, (S-1) is a composite system

In this chapter, we give a brief introduction into the use of the Zeeman effect in astronomy and the general detection of magneticfields in stars, concentrating on the use of FORS2 for longitudinal magneticfield measurements.

The magnetism of single atoms and molecules is governed by the atomic scale environment. In general, the reduced symmetry of the surrounding splits the d states and aligns the magnetic moment along certain favorable directions. Here, we show that we can reversibly modify the magnetocrystalline anisotropy by manipulating the environment of single iron(II) porphyrin molecules adsorbed on Pb(111) with the tip of a scanning tunneling microscope. When we decrease the tip-molecule distance, we first observe a small increase followed by an exponential decrease of the axial anisotropy on the molecules. This is in contrast to the monotonous increase observed earlier for the same molecule with an additional axial Cl ligand ( Nat. Phys. 2013 , 9 , 765 ). We ascribe the changes in the anisotropy of both species to a deformation of the molecules in the presence of the attractive force of the tip, which leads to a change in the d level alignment. These experiments demonstrate the feasibility of a precise tuning of the magneticanisotropy of an individual molecule by mechanical control. PMID:25942560

The magnetic behavior of polycrystalline samples of Er2Ir2O7 and Tb2Ir2O7 pyrochlores is studied by magnetization measurements and neutron diffraction. Both compounds undergo a magnetic transition at 140 and 130 K, respectively, associated with an ordering of the Ir sublattice, signaled by thermomagnetic hysteresis. In Tb2Ir2O7 , we show that the Ir molecular field leads the Tb magnetic moments to order below 40 K in the all-in-all-out magnetic arrangement. No sign of magnetic long-range order on the Er sublattice is evidenced in Er2Ir2O7 down to 0.6 K where a spin freezing is detected. These contrasting behaviors result from the competition between the Ir molecular field and the different single-ion anisotropy of the rare-earth elements on which it is acting. Additionally, this strongly supports the all-in-all-out iridium magnetic order.

The magneticanisotropy of cobalt ferrite is considered to arise from the cobaltous ions in the crystalline field of a low symmetry. The crystalline field due to the averaged-out charge distribution of Co^{2+} and Fe^{3+} ions in the octahedral sites gives the lowest-lying twofold degenerate orbital level of the Co^{2+} ion and to this level are associated four spin levels,

3-D printing processes, which use drop-on-demand inkjet printheads, have great potential in designing and prototyping magnetic materials. Unlike conventional deposition and lithography, magnetic particles in the printing ink can be aligned by an external magneticfield to achieve both high permeability and low hysteresis losses, enabling prototyping and development of novel magnetic composite materials and components, e.g., for inductor and antennae applications. In this work, we report an inkjet printing technique with magnetic alignment capability. Magnetic films with and without particle alignment are printed, and their magnetic properties are compared. In the alignment-induced hard axis direction, an increase in high frequency permeability and a decrease in hysteresis losses are observed. Our results suggest that unique magnetic structures with arbitrary controllable anisotropy, not feasible otherwise, may be fabricated via inkjet printing.

Co-23-wt. %-Cr alloy films with thicknesses of 0.3 to 2.5 ?m were deposited using a conventional rf diode sputtering system when a magneticfield Hs less than 90 Oe is applied during deposition. As Hs increases, the hcp c-axis orientation normal to the film plane develops and the half-angle width of the rocking curve of the (002) line ??50 reaches to 3.5 deg at Hs more than 40 Oe. The development of the orientation is strongly related to the concentration of O in the films, which is lower in the films deposited in a magneticfield than those in a nonmagnetic field. The magnetic properties such as perpendicular coercive force Hc? and saturation magnetization Ms strongly depend on the substrate temperature rather than Hs.

The anisotropy of magnetic susceptibility (AMS) of single crystals of biotite, muscovite and chlorite has been measured in order to provide accurate values of the magneticanisotropy properties for these common rock-forming minerals. The low-field AMS and the high-field paramagnetic susceptibility are defined. For the high-field values, it is necessary to combine the paramagnetic deviatoric tensor obtained from the high-field

The anisotropies in the pressure obtained from the energy-momentum tensor are studied for magnetized quark matter within the su(3) Nambu-Jona-Lasinio model for both $\\beta$-equilibrium matter and quark matter with equal quark chemical potentials. The effect of the magneticfield on the particle polarization, magnetization and quark matter constituents is discussed. It is shown that the onset of the $s$-quark after chiral symmetry restoration of the $u$ and $d$-quarks gives rise to a special effect on the magnetization in the corresponding density range: a quite small magnetization just before the $s$ onset is followed by a strong increase of this quantity as soon as the $s$ quark sets in. It is also demonstrated that for $B<10^{18}$ G within the two scenarios discussed, always considering a constant magneticfield, the two components of pressure are practically coincident.

The anisotropies in the pressure obtained from the energy-momentum tensor are studied for magnetized quark matter within the su(3) Nambu-Jona-Lasinio model for both ? -equilibrium matter and quark matter with equal quark chemical potentials. The effect of the magneticfield on the particle polarization, magnetization, and quark matter constituents is discussed. It is shown that the onset of the s quark after chiral symmetry restoration of the u and d quarks gives rise to a special effect on the magnetization in the corresponding density range: A quite small magnetization just before the s onset is followed by a strong increase of this quantity as soon as the s quark sets in. It is also demonstrated that for B <1018 G within the two scenarios discussed, always considering a constant magneticfield, the two components of pressure are practically coincident.

A modified version of the Stoner-Wohlfarth model, which takes into account thermal effects, has been used to study the influence of measuring temperature on the magneticanisotropy derived from demagnetization curves. To be able to reproduce the thermal dependence of the magnetization curve, and not only of coercivity, a Neel relaxation approach is considered, avoiding the two-state approximation. Anisotropy results are compared with calculations for field and temperature dependent torque magnetometry, indicating that the most reliable parameter in the apparent distribution of anisotropy is the mean value of the anisotropyfield.

Field-induced magnetic ordering in the Haldane chain compound SrNi2V2O8 and the effect of anisotropy have been investigated using single crystals. Static susceptibility, inelastic neutron scattering, high-fieldmagnetization, and low-temperature heat-capacity studies confirm a nonmagnetic spin-singlet ground state and a gap between the singlet ground state and triplet excited states. The intrachain exchange interaction is estimated to be J8.9±0.1 meV. Splitting of the dispersions into two modes with minimum energies 1.57 and 2.58 meV confirms the existence of single-ion anisotropy D(Sz)2. The value of D is estimated to be -0.51±0.01 meV and the easy axis is found to be along the crystallographic c axis. Field-induced magnetic ordering has been found with two critical fields (?0Hc?c=12.0±0.2 T and ?0Hc?c=20.8±0.5 T at 4.2 K). Field-induced three-dimensional magnetic ordering above the critical fields is evident from the heat-capacity, susceptibility, and high-fieldmagnetization study. The phase diagram in the H-T plane has been obtained from the high-fieldmagnetization. The observed results are discussed in the light of theoretical predictions as well as earlier experimental reports on Haldane chain compounds.

Polymeric microcomponents are widely used in microelectromechanical systems (MEMS) and lab-on-a-chip devices, but they suffer from the lack of complex motion, effective addressability and precise shape control. To address these needs, we fabricated polymeric nanocomposite microactuators driven by programmable heterogeneous magneticanisotropy. Spatially modulated photopatterning was applied in a shape-independent manner to microactuator components by successive confinement of self-assembled magnetic nanoparticles in a fixed polymer matrix. By freely programming the rotational axis of each component, we demonstrate that the polymeric microactuators can undergo predesigned, complex two- and three-dimensional motion. PMID:21822261

Context. Interstellar grain alignment studies are currently experiencing a renaissance due to the development of a new quantitative theory based on radiative alignment torques (RAT). One of the distinguishing predictions of this theory is a dependence of the grain alignment efficiency on the relative angle (?) between the magneticfield and the anisotropy direction of the radiation field. In an earlier study we found observational evidence for such an effect from observations of the polarization around the star HD 97300 in the Chamaeleon I cloud. However, due to the large uncertainties in the measured visual extinctions, the result was uncertain. Aims: By acquiring explicit spectral classification of the polarization targets, we have sought to perform a more precise reanalysis of the existing polarimetry data. Methods: We have obtained new spectral types for the stars in our for our polarization sample, which we combine with photometric data from the literature to derive accurate visual extinctions for our sample of background field stars. This allows a high accuracy test of the grain alignment efficiency as a function of ?. Results: We confirm and improve the measured accuracy of the variability of the grain alignment efficiency with ?, seen in the earlier study. We note that the grain temperature (heating) also shows a dependence on ? which we interpret as a natural effect of the projection of the grain surface to the illuminating radiation source. This dependence also allows us to derive an estimate of the fraction of aligned grains in the cloud.

Fe40Co60 epitaxial thin films are prepared on L10 ordered Fe60Pt40 underlayer by ultrahigh vacuum multiple dc-sputtering systems. Magnetic properties of the Fe60Pt40 (10 nm)/Fe40Co60 (t nm) bilayer films are investigated. When the FeCo thickness is less than 3 nm, the easy magnetization axis of FePt/FeCo bilayer film is perpendicular to the film plane. Compared with FePt/Fe and FePt/Co films, FePt/FeCo bilayer films possess not only higher anisotropyfield Hk but also larger magneticanisotropy energy Ku, which may be due to the perpendicular magneticanisotropy yielded by the tetragonal distorted FeCo layer on FePt, while the magnetic easy axes of Fe and Co layers lie in the film plane. Meanwhile, saturation magnetization of FePt/FeCo film increases reasonably because of the high Ms value of FeCo component. These results indicate that the FePt/FeCo bilayer films which possess both large magneticanisotropy energy Ku and high saturation magnetization Ms have great potential for using as the magnetic recording media, and also give a clue to develop a new type of permanent magnet without rare-earth metals.

A new technique involving magnetization measurements on a rotating sample in a cryogenic magnetometer with variable field, from 0 to 4 T, and variable temperature is presented. It can be used to separate and identify multi-component anisotropy in rocks. The results obtained for anisotropy due to magnetite, haematite, pyrrhotite or phyllosilicates are interpreted according to different magnetization models.

Measurement of the magneto-optical polar Kerr effect is performed on rare earth-transition metal (RE-TM) amorphous films using in-plane fields. From this measurement and the measurement of the saturation magnetization using a vibrating sample magnetometer (VSM), the magneticanisotropy constants are determined. The temperature dependence is presented of the magneticanisotropy in the range of -175 to 175 C. The results show a dip in the anisotropy near magnetic compensation. This anomaly is explained based on the finite exchange coupling between the rare earth and transition metal subnetworks.

The time and field dependence of the magnetic domain structure at magnetization reversal were investigated by Kerr microscopy in a structure consisting of a hard and a soft ferromagnetic Co\\/Pt multilayer stack with perpendicular anisotropy, separated by a thicker nonmagnetic Pt spacer layer. Large local inhomogeneous magnetostatic stray fields appear as soon as a nonuniform magnetic area exists within one

Low loss switching of soft magnetic materials at high frequencies benefits from tuning the induced anisotropy. We show induced anisotropies, Ku, as large as 1.89×104 J /m3, developed by strain annealing of Co-rich nanocomposite alloys. Crystalline phases in this alloy system have large negative magnetostrictive coefficients, leading to anisotropyfields per unit stress over twice those developed in FINEMET. Tunable permeability and reduced thicknesses achieved in this process can mitigate eddy-current losses. Giant induced magneticanisotropies are discussed in light of models for the micromechanisms of amorphous metal deformation, stress-assisted transformations in the crystallites, and directional pair ordering.

In the Neoproterozoic East African Orogen (EAO) of Eritrea, lower to middle crustal high-grade metamorphic rocks are juxtaposed against low-grade upper crustal rocks along diffuse tectonic contact zones or discontinuities. In the central eastern part of Eritrea, such a tectonic zone is exposed as a low-angle shear zone separating two distinct high- and low-grade domains, the Ghedem and Bizen, respectively. Integrated field, microfabric, and anisotropy of magnetic susceptibility (AMS) studies show that this low-angle shear zone formed during late deformation, D2, with top-to-the-E/SE sense of motion. The hanging wall upper crustal volcanosedimentary schists are mainly paramagnetic and the footwall middle crustal mylonitized orthogneisses are mainly ferrimagnetic. Magnetic fabric studies revealed a good agreement between metamorphic/mylonitic and magnetic foliations (Kmin) and helped to explain fabric development in the shear zone. The magnetic lineations (Kmax) reflect stretching lineations where stretched mineral aggregates dominate fine-grained mylonitic matrices and intersection lineations where microstructural studies revealed two fabric elements. AMS directional plots indicate that the orientations of the magnetic lineation and of the pole to the magnetic foliation vary systematically across the shear zone. While Kmax axes form two broad maxima oriented approximately N-S and E-W, the Kmin axes change from subhorizontal, generally westward inclination in the west to moderate to steep inclination in the direction of tectonic movement to the east. Because there is a systematic change in inclination of Kmin for individual samples, all samples together form a fairly well defined cluster distribution. The distribution of Kmin in combination with the E-W scattered plot of the Kmax is in accordance with the E/SE flow of mylonites over exhumed Damas core complex in the late Neoproterozoic. During the Cenozoic, the Red Sea rift-related detachments exploited the late orogenic shear zone, indicating that the discontinuities between ductile middle and brittle upper crustal layers in the region are reactivated low-angle shear zones and possible sites of core complexes.

Anisotropic x-ray magnetic linear dichroism (AXMLD) provides a novel element-, site-, shell-, and symmetry-selective techniques to study the magneticanisotropy induced by a crystalline electric field. The weak Eu2+ M4,5 AXMLD observed in EuO(001) indicates that the Eu 4f states are not rotationally invariant and hence contribute weakly to the magneticanisotropy of EuO. The results are contrasted with those obtained for 3d transition metal oxides.

High-field, angle-dependent x-ray magnetic circular dichroism measurements on a Au/Co-staircase/Au structure reveal an anisotropy in the dichroism intensities parallel and perpendicular to the film plane. The size of this effect is related to the anisotropies of the spin density within the Wigner-Seitz cell and of the orbital magnetic moment, both increasing with decreasing Co thickness. The orbital moment anisotropy is shown to be the microscopic origin of the magnetocrystalline energy anisotropy. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

Being able to control the anisotropy of a magnetic core plays an important role in the development of a fluxgate sensor. Our aim is to induce anisotropy orthogonal to the direction of excitation because it generates a stable, low-noise fluxgate, as cited in the literature. In this paper, we present an original method for electroplating a ring core for a fluxgate with built-in radial anisotropy by performing the electroplating in a radial field produced by a novel yoke. The results show that the resulting anisotropy is homogeneously radial and makes the magnetization rotate, avoiding domain wall movement for low excitation fields.

The exchange bias in a soft ferromagnetic NiFe layer coupled with a hard ferrimagnetic Fe3O4 film grown on a (110) SrTiO3 single-crystal substrate was investigated as a function of the switching magneticfield (HS) as a means to control the magnetization direction of the Fe3O4. The sign of the exchange bias was consistent with the sign of HS, indicating that the exchange coupling constant between the NiFe and (110) Fe3O4 layers was positive. Below |HS| = 1 kOe, the hysteresis behavior of the exchange bias of the soft ferromagnetic NiFe resembled the magnetic hysteresis behavior of the hard ferrimagnetic Fe3O4.

Co-doped SnO2 thin films were grown by sputtering technique on SiO2/Si(001) substrates at room temperature, and then, thermal treatments with and without an applied magneticfield (HTT) were performed in vacuum at 600°C for 20 min. HTT was applied parallel and perpendicular to the substrate surface. Magnetic M(H) measurements reveal the coexistence of a strong antiferromagnetic (AFM) signal and a ferromagnetic (FM) component. The AFM component has a Néel temperature higher than room temperature, the spin axis lies parallel to the substrate surface, and the highest magnetic moment m =7 ?B/Co at. is obtained when HTT is applied parallel to the substrate surface. Our results show an enhancement of FM moment per Co+2 from 0.06 to 0.42 ?B/Co at. for the sample on which HTT was applied perpendicular to the surface. The FM order is attributed to the coupling of Co+2 ions through electrons trapped at the site of oxygen vacancies, as described by the bound magnetic polaron model. Our results suggest that FM order is aligned along [101] direction of Co-doped SnO2 nanocrystals, which is proposed to be the easy magnetization axis.

Co-doped SnO2 thin films were grown by sputtering technique on SiO2/Si(001) substrates at room temperature, and then, thermal treatments with and without an applied magneticfield (HTT) were performed in vacuum at 600°C for 20 min. HTT was applied parallel and perpendicular to the substrate surface. Magnetic M(H) measurements reveal the coexistence of a strong antiferromagnetic (AFM) signal and a ferromagnetic (FM) component. The AFM component has a Néel temperature higher than room temperature, the spin axis lies parallel to the substrate surface, and the highest magnetic moment m =7 ?B/Co at. is obtained when HTT is applied parallel to the substrate surface. Our results show an enhancement of FM moment per Co+2 from 0.06 to 0.42 ?B/Co at. for the sample on which HTT was applied perpendicular to the surface. The FM order is attributed to the coupling of Co+2 ions through electrons trapped at the site of oxygen vacancies, as described by the bound magnetic polaron model. Our results suggest that FM order is aligned along [101] direction of Co-doped SnO2 nanocrystals, which is proposed to be the easy magnetization axis. PMID:25489286

The anisotropy of susceptibility of metamorphic rocks can be due to paramagnetic rock-forming silicates such as amphiboles, chlorites and micas. It is not always necessary to invoke fabrics of separate grains of iron oxide to explain the anisotropy. Minimum estimates of lattice anisotropies of typical samples of silicates have maximum-to-minimum ratios of 1.1-1.7. Since the magneticanisotropies of most metamorphic

Magnetoelectric phenomena become one of the most attractive fields of magnetism. One of discussable items is inhomogeneous magnetoelectricity leading to appearance of electric polarization of magnetic domain walls, improper polarization of multiferroics etc. In our article we attract attention to the modulation of electric polarization by magnetic inhomogeneity in exchange coupled ferromagnetic film whose layers differ by magneticanisotropy. Our goal is to explore the influence of combined magneticanisotropy (especially its cubic component) on the behavior of electric polarization of bi-layered film placed in magneticfield. We perform theoretical analysis in a frame of phenomenological modeling of spins structures considering two geometries of magneticfield (magneticfield oriented perpendicular to a film plane and magneticfield oriented in a film plane along "hard magnetization" axis). Our results show that the presence of cubic magneticanisotropy (Kc<0) in the layers allocates the planes of magnetic inhomogeneities and correspondingly the directions of electric polarization. We demonstrate that magneticfield applied along the "hard magnetization" axis leads to the rotation of electric polarization in the 45° range and magneticfield applied along normal to a film influences the magnitude of electric polarization leading to the lowering of polarization after attaining the maximum value.

We present experimental 2D vector vibrating sample magnetometer measurements to demonstrate the shape anisotropy effects occurring in micrometer-diameter supermalloy spin vortex discs. Measurements made for different disc sizes and orientations confirm the out-of-plane susceptibility is several orders of magnitude smaller than the in-plane susceptibility. These results validate with a high certitude that spin vortices with high diameter to thickness ratio retain in-plane-only magnetization, even when subjected to fields in the out-of-plane direction. These results contribute to further computational simulations of the dynamics of spin vortex structures in colloidal suspensions where external fields may be applied in any arbitrary direction.

We present experimental 2D vector vibrating sample magnetometer measurements to demonstrate the shape anisotropy effects occurring in micrometer-diameter supermalloy spin vortex discs. Measurements made for different disc sizes and orientations confirm the out-of-plane susceptibility is several orders of magnitude smaller than the in-plane susceptibility. These results validate with a high certitude that spin vortices with high diameter to thickness ratio retain in-plane-only magnetization, even when subjected to fields in the out-of-plane direction. These results contribute to further computational simulations of the dynamics of spin vortex structures in colloidal suspensions where external fields may be applied in any arbitrary direction.

: magnetocrystalline anisotropy, demagnetizing field energy (shape anisot- ropy), magnetoelastic (ME) coupling energyInterplay between Anisotropic Strain Relaxation and Uniaxial Interface MagneticAnisotropy an anisotropy of both domain shape and strain, with [110] and [1-10] as the principal directions. It is shown

We present our extensive research into magneticanisotropy. We tuned the terrace width of Si(111) substrate by a novel method: varying the direction of heating current and consequently manipulating the magneticanisotropy of magnetic structures on the stepped substrate by decorating its atomic steps. Laser-induced ultrafast demagnetization of a CoFeB/MgO/CoFeB magnetic tunneling junction was explored by the time-resolved magneto-optical Kerr effect (TR-MOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electron tunneling current. This opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions. Furthermore, an all-optical TR-MOKE technique provides the flexibility for exploring the nonlinear magnetization dynamics in ferromagnetic materials, especially with metallic materials. Project supported by the National Basic Research Program of China (Grant Nos. 2015CB921403, 2011CB921801, and 2012CB933101) and the National Natural Science Foundation of China (Grant Nos. 51427801, 11374350, 51201179, and 11274361).

Superconducting magnets with magneticfields above 20 T will be needed for a Muon Collider and possible LHC energy upgrade. This field level exceeds the possibilities of traditional Low Temperature Superconductors (LTS) such as Nb{sub 3}Sn and Nb{sub 3}Al. Presently the use of high field high temperature superconductors (HTS) is the only option available for achieving such field levels. Commercially available YBCO comes in tapes and shows noticeable anisotropy with respect to field orientation, which needs to be accounted for during magnet design. In the present work, critical current test results are presented for YBCO tape manufactured by Bruker. Short sample measurements results are presented up to 14 T, assessing the level of anisotropy as a function of field, field orientation and operating temperature.

interpreted as because of the dominance of magnetoelastic energy over the magnetocrystalline anisotropy energyImaging the magnetization reversal of step-induced uniaxial magneticanisotropy in vicinal of step-induced uniaxial magneticanisotropy in vicinal epitaxial La0.7Sr0.3MnO3 films P Perna1,2,4 , L

Existing approaches for prediction of the tensor permeability of polycrystalline ferrites may not provide reasonable estimates of demagnetized permeability below the spin resonance (i.e., low-field loss region) or in cases of partial magnetization. We propose an approach which solves the coupled Landau-Lifshitz-Gilbert equation for the dynamic magneticfields including the minimization of free energy to determine the equilibrium magnetization direction. Unlike previous models, we employ a Monte-Carlo approach to easily calculate the (ensemble) averages of permeability over various domain/grain structures and magneticanisotropy conditions. Material differences, such as those resulting from different preparation methods, are expressed by using probability density functions (p.d.f.) for anisotropy angle (easy axis angle), grain demagnetization factor (ng), and domain demagnetization factor (nd). Effects on the permeability tensor of grain and domain demagnetization factors and anisotropyfield relative to saturation magnetization are discussed for the partially magnetized states for polycrystalline ferrites. It is found that the grain structure (i.e., grain demagnetization distribution) has a smaller effect on the frequency dependent permeability than does the same distribution of domains (i.e., domain demagnetization distribution).

Molecules trapped in single-molecule devices vibrate with discrete frequencies characteristic to the molecules, and the molecular vibrations can couple to electronic charge and/or spin degrees of freedom. For a significant electron-vibron coupling, electrons may tunnel via the vibrational excitations unique to the molecules. Recently, electron transport via individual anisotropic magnetic molecules (referred to as single-molecule magnets) has been observed in single-molecule transistors. A single-molecule magnet has a large spin moment and a large magneticanisotropy barrier. So far, studies of electron-vibron coupling effects in single-molecule devices, are mainly for isotropic molecules. Here we investigate how the electron-vibron coupling influences electron transport via a single-molecule magnet Fe4, by using a model Hamiltonian with parameter values obtained from density-functional theory (arXiv:1411.2677). We show that the magneticanisotropy of the Fe4 induces new features in vibrational conductance peaks and creates vibrational satellite peaks. The main and satellite peak heights have a strong, unusual dependence on the direction and magnitude of applied magneticfield, because the magneticanisotropy barrier is comparable to vibrational energies. Funding from NSF DMR-1206354, EU FP7 program project 618082 ACMOL, advanced ERC grant (Mols@Mols). Computer resources from SDSC Trestles under DMR060009N and VT ARC.

The magnetic behavior of polycrystalline samples of Er_{2}Ir_{2}O_{7} and Tb_{2}Ir_{2}O_{7} pyrochlores is studied by magnetization measurements and neutron diffraction. Both compounds undergo a magnetic transition at 140 and 130 K, respectively, associated with an ordering of the Ir sublattice, signaled by thermomagnetic hysteresis. In Tb_{2}Ir_{2}O_{7}, we show that the Ir molecular field leads the Tb magnetic moments to order below 40 K in the all-in-all-out magnetic arrangement. No sign of magnetic long-range order on the Er sublattice is evidenced in Er_{2}Ir_{2}O_{7} down to 0.6 K where a spin freezing is detected. These contrasting behaviors result from the competition between the Ir molecular field and the different single-ion anisotropy of the rare-earth elements on which it is acting. Additionally, this strongly supports the all-in-all-out iridium magnetic order. PMID:26197002

We demonstrate that a C60 overlayer enhances the perpendicular magneticanisotropy of a Co thin film, inducing an inverse spin reorientation transition from in plane to out of plane. The driving force is the C60/Co interfacial magneticanisotropy that we have measured quantitatively in situ as a function of the C60 coverage. Comparison with state-of-the-art ab initio calculations show that this interfacial anisotropy mainly arises from the local hybridization between C60 pz and Co dz2 orbitals. By generalizing these arguments, we also demonstrate that the hybridization of C60 with a Fe(110) surface decreases the perpendicular magneticanisotropy. These results open the way to tailor the interfacial magneticanisotropy in organic-material-ferromagnet systems.

Influence of magnetic interactions on the Anisotropy of Magnetic Susceptibility: The case of single The influence of magnetic interactions on the anisotropy of magnetic susceptibility (AMS) have been largely control the AMS. We have shown recently from a comprehensive rock magnetic study and from a theoretical 2

Measuring magnetocrystalline anisotropyfield distribution of patterned magnetic nanodots using a microscopically visualizing way is important for understanding some important magnetic behaviors such as switching field distribution (SFD) of patterned recording media. We present a detailed analysis of the remanent domain structures of L10-FePt triangular nanodots as revealed by high resolution magnetic force microscopy (MFM) with the help of micromagnetic simulation, showing that the domain structure diversity can effectively account for a dot-to-dot variation of the magnetocrystalline anisotropyfield. Our method could shed light not only on understanding the fundamental causes of a wider SFD but also on designing future nanostructured magnetic devices.

Magneticanisotropy is investigated systematically for the textured MnBi crystal. The magneticanisotropy exists in magnetization behaviors, hysteresis loops, and remnant magnetization. An abnormal coercivity field Hc is found in the textured MnBi: Hc perpendicular to the c-axis is larger than that parallel to the c-axis. The mechanism of anisotropy is discussed based on magnetocrystalline anisotropy in MnBi. The behavior of a.c. susceptibility has similar trends with frequency variation, not displaying a spin-disorder characteristic. The MnBi with ferromagnetic order has a higher loss under high frequencies than under low frequencies. Some spin-reorientation evidence in the MnBi is also obtained.

Three-dimensional antiferromagnets with random magneticanisotropy (RMA) that have been experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of Fe_{x}Ni_{1-x}F_{2} epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean-field theory. Regions with uniaxial, oblique, and easy-plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs. PMID:25793845

Although boron-free FeCo films prepared on a Ru underlayer exhibits isotropic in-plane magnetic property, boron added FeCoB films prepared on Ru underlayer revealed large in-plane magneticanisotropy with a high anisotropyfield of 500 Oe. The effect of boron addition on the in-plane anisotropic residual stress in FeCoB film was investigated using sin{sup 2} {psi} method of x-ray diffraction analysis. Large isotropic compressive stress was observed in Ru/FeCo film. In contrast, anisotropic in-plane residual stress was observed in Ru/FeCoB film. The compressive stress along the easy axis of Ru/FeCoB film is released more than that along the hard axis. Such anisotropic residual stress is regarded as an origin of the in-plane magneticanisotropy through inverse magnetostriction effect. Owing to the configuration of the facing targets sputtering system, boron atoms are sputtered and deposited anisotropically, and so they penetrate FeCo crystals and release the compressive stress along the incidence direction.

Mn3O4 has Yafet-Kittel type spin structure below Neel Temperature (41K). The magnetization along the c-axis is smaller than that along the ab-plane even in external magneticfield of 30 Tesla, implying huge magneticanisotropy in the ab-plane. We measured ^55Mn^2+ and ^55Mn^3+ Nuclear Magnetic Resonance (NMR) of a Mn3O4 single crystal in external magneticfield. The canting angles of Mn^2+ and Mn^3+ magnetic moments were calculated from the spectral shift obtained for various magneticfield directions between the a, b and c-axes. With the canting angle data, we estimated the anisotropy energies of the Mn^2+ and Mn^3+ magnetic moments and the exchange energy between them. The result also shows that Mn^3+ spins in the Yafet-Kittel structure lie in the ab-plane contrary to the previous reports.

Magnetization hysteresis curves have been measured on Co granular multilayers, (Al2O3/Co/Pt)N (N = 1 and 25), with the applied magneticfield parallel and perpendicular to the substrate plane. In all samples perpendicular magneticanisotropy was observed. For Co particles with average diameter 3 nm, the coercive field at low temperature is ?0HC = 0.5 T. HC decreases for increasing temperature and disappears at ?200 K. A soft magnetic component is also present in all samples up to the freezing temperature Tf = 365 K. Co and Pt XMCD measurements at the L2,3 edges were performed, yielding to the orbital mL and spin mS contributions to the total magnetic moment of the system. These results, in addition to XANES ones, indicate the presence of CoxPt1-x alloy. Particles conformed of CoPt alloy, embedded in Pt and coupled magnetically by dipolar or RKKY interaction, may explain the phenomenology observed in these systems.

The magneticanisotropy is decreased with increasing temperature in normal magnetic materials, which is harmful to the thermal stability of magnetic devices. Here, we report the realization of positive temperature coefficient of magneticanisotropy in a novel composite combining ?-phase polyvinylidene fluoride (PVDF) with magnetostrictive materials (magnetostrictive film/PVDF bilayer structure). We ascribe the enhanced magneticanisotropy of the magnetic film at elevated temperature to the strain-induced anisotropy resulting from the anisotropic thermal expansion of the ?-phase PVDF. The simulation based on modified Stoner-Wohlfarth model and the ferromagnetic resonance measurements confirms our results. The positive temperature coefficient of magneticanisotropy is estimated to be 1.1 × 102?J m?3 K?1. Preparing the composite at low temperature can enlarge the temperature range where it shows the positive temperature coefficient of magneticanisotropy. The present results may help to design magnetic devices with improved thermal stability and enhanced performance. PMID:25311047

Magneticfield-structured-composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g. rotating) magneticfields, while polymerizing the suspending resin. A uniaxial field produces chain-like particle structures, and a biaxial field produces sheet-like particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCS of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material.

The anisotropy of magnetic susceptibility (AMS) is an integral measure of the preferred orientation of all minerals present in a rock. When the AMS is carried by paramagnetic minerals alone, the principal directions of the susceptibility ellipsoid should reflect the crystallographic orientation of the minerals. The relationship between the AMS and deformation depends on several factors, which control the development of lattice-preferred orientation (LPO) in a rock. A mathematical model is presented that simulates the magnetic susceptibility ellipsoid for samples composed of more than one mineral phase. Measurements of the AMS are compared with fabric-based anisotropy models for black slates from the Navia-Alto Sil slate belt in northern Spain. The AMS is carried by paramagnetic minerals, as has been confirmed by high-field torque magnetometry, low-temperature AMS and magnetization curves. The LPO of mica and chlorite has been determined by X-ray texture goniometry. Pole figures and orientation ellipsoids show the changes in the degree of alignment of the phyllosilicates. The models have been tested in samples displaying three types of pole figures: a high-intensity point maximum, a medium-intensity elliptical maximum, and a girdle-shaped distribution. At one site displaying kink bands the LPO shows variations between these types at the outcrop scale. The case studies illustrate the success in modeling different LPO types.

The magneticanisotropy of Co/Pt/FeMn multilayers grown onto two-dimensional arrays of nanospherical polystyrene particles is studied at room temperature using Ferromagnetic Resonance measurements with X-band microwave frequency. The in-plane and out-of-plane resonance spectra display two uniform absorption modes due to two distinct magnetic phases, revealing an inhomogeneous magnetization profile through the thickness and at the top and the equator of the magnetic caps. The in-plane measurements of the angular dependence of the two absorption fields reveal that the distinct magnetic phases exhibit the effects of twofold and fourfold magneticanisotropyfields. Out-of-plane measurements show that the magnetization of each magnetic phase depends on the structure of the multilayer and is oriented at a specific direction oblique to the plane of the film.

The effect of buffer layer on the magneticanisotropy of Fe film has been investigated by using the planar Hall effect measurement. The Fe films were grown on four different buffer layers, such as GaAs, ZnSe, ZnTe, and Ge, by molecular beam epitaxy. The field and angle dependent planar Hall effect measurements revealed the presence of two types of magneticanisotropies, i.e., cubic crystalline anisotropy along the <100> directions and uniaxial anisotropy along the <110> crystallographic directions, in all four Fe films investigated in the study. However, the relative strength of the two types of anisotropies varies significantly depending on the type of buffer layer. Specially, in the Fe film grown on the Ge buffer layer, the uniaxial anisotropy almost disappeared and the entire magneticanisotropy was dominated by cubic anisotropy with a four-fold symmetry. This suggests that the growth of Fe film on the Ge surface is different from its growth on other surfaces such as GaAs, ZnSe, and ZnTe buffers, where the asymmetric reconstruction process of anions (i.e., As, Se, or Te) is present at the surface.

Interconnected or crossed magnetic nanowire networks have been fabricated by electrodeposition into a polycarbonate template with crossed cylindrical nanopores oriented ±30° with respect to the surface normal. Tailor-made nanoporous polymer membranes have been designed by performing a double energetic heavy ion irradiation with fixed incidence angles. The Ni and Ni/NiFe nanowire networks have been characterized by magnetometry as well as ferromagnetic resonance and compared with parallel nanowire arrays of the same diameter and density. The most interesting feature of these nanostructured materials is a significant reduction of the magneticanisotropy when the external field is applied perpendicular and parallel to the plane of the sample. This effect is attributed to the relative orientation of the nanowire axes with the applied field. Moreover, the microwave transmission spectra of these nanowire networks display an asymmetric linewidth broadening, which may be interesting for the development of low-pass filters. Nanoporous templates made of well-defined nanochannel network constitute an interesting approach to fabricate materials with controlled anisotropy and microwave absorption properties that can be easily modified by adjusting the relative orientation of the nanochannels, pore sizes and material composition along the length of the nanowire. PMID:25501534

We present a first-principles investigation of the electronic structure and physical properties of doped lithium nitridometalates Li2(Li1-xMx)N (LiMN) with M = Cr, Mn, Fe, Co, and Ni. The diverse properties include the equilibrium magnetic moments, magneto-crystalline anisotropy, magneto-optical Kerr spectra, and x-ray magnetic circular dichroism. We explain the colossal magneticanisotropy in LiFeN by its unique electronic structure which ultimately leads to a series of unusual physical properties. The most unique property is a complete suppression of relativistic effects and freezing of orbital moments for in-plane orientation of the magnetization. This leads to the colossal spatial anisotropy of many magnetic properties including energy, Kerr, and dichroism effects. LiFeN is identified as an ultimate single-ion anisotropy system where a nearly insulating state can be produced by a spin orbital coupling alone. A very nontrivial strongly fluctuating and sign changing character of the magneticanisotropy with electronic 3d-atomic doping is predicted theoretically. A large and highly anisotropic Kerr effect due to the interband transitions between atomic-like Fe 3d bands is found for LiFeN. A giant anisotropy of the x-ray magnetic circular dichroism for the Fe K spectrum and a very weak one for the Fe L2,3 spectra in LiFeN are also predicted.

In the era of spin-based advanced semiconductor materials, spin can be used for the control of quantum devices based on quantum dots (QDs). To facilitate the control of the electronic and magnetic properties, magnetic ions can be incorporated in the QDs. We study the properties of such a magnetic II-VI QD charged with one hole. To account for the complex structure of valence band, we propose a method based on the Luttinger-Kohn Hamiltonian. With a robust numerical algorithm suitable for any QD geometry, we study the interplay of quantum confinement and magneticanisotropy of a flat QD. We go beyond the virtual crystal approximation; our model also allows for position-dependent direction of magnetization. We discuss the differences between our and previous results, as well as the effects of temperature (mean-field approximation), and of the spin-orbit split-off band. We also discuss possible fluctuations of magnetization in QDs. Supported by DOE DE-SC00004890. DoE

The use of processing techniques to create magneticanisotropy in soft magnetic materials is a well-known method to control permeability and losses. In nanocomposite materials, field annealing below the Curie temperature results in uniaxial anisotropy energies up to 2 kJ/m3. Higher anisotropies up to 10 kJ/m3 result after annealing Fe-Si compositions under stress due to residual stress in the amorphous matrix acting on body centered cubic crystals. This work describes near zero magnetostriction Co80-x-yFexMnyNb4B14Si2 soft magnetic nanocomposites, where x and y < 8 at.% with close packed crystalline grains that show stress induced anisotropies up to 50 kJ/m3 and improved mechanical properties with respect to Fe-Si compositions. Difference patterns measured using transmission X-ray diffraction show evidence of affine strain with respect to the stress axis.

High-spin paramagnetic manganese defects in polar piezoelectric zinc oxide exhibit a simple almost axial anisotropy and phase coherence times of the order of a millisecond at low temperatures. The anisotropy energy is tunable using an externally applied electric field. This can be used to control electrically the phase of spin superpositions and to drive spin transitions with resonant microwave electric fields.

Several types of magnetic films containing rare earth and\\/or transition metals are made by dc magnetron sputtering. Deposition conditions are varied and underlayers are used to control the magneticanisotropy respective to the film geometry. In the case of Co\\/Cr multilayers, in-plane anisotropy is obtained with high coercivity over a wide range of Co and Cr thicknesses. The deposition conditions

LETTERS The role of magneticanisotropy in the Kondo effect ALEXANDER F. OTTE1,2 , MARKUS TERNES11072 In the Kondo effect, a localized magnetic moment is screened by forming a correlated electron system with the surrounding conduction electrons of a non-magnetic host1 . Spin S = 1/2 Kondo systems

Induced and remanent magnetic analyses have been performed on drilled samples from 2 generations of unweathered diabase dikes, a breccia dike, and the host tonalite which make up the basement on which the Russell Dam foundation was poured. The maximum magnetic foliation plane for most samples, defined by anisotropy of magnetic susceptibility (AMS) data, is vertical and is oriented perpendicular

The magneticanisotropy of the whole radula, the major lateral radula teeth, and magnetic material in the major lateral radula teeth of the chiton Acanthochiton rubrolinestus LISCHKE have been studied by a magnetic torque meter and superconducting quantum interference device (SQUID) magnetometer. The length and width axes of the teeth are the easily magnetized axes, while the thickness axis is difficult to magnetize. The width and thickness axes of the radula are the easily magnetized axes, and the length axis is difficult to magnetize. The measurement results of the whole radula and the major lateral radula teeth agree well with each other. The magneticanisotropy of the magnetic material is given as well as a possible distribution of the magnetic material in the major lateral radula teeth. PMID:12210567

Atomic Force Microscopy and Grazing incidence X-ray diffraction measurements have revealed the presence of ripples aligned along the $[1\\bar{1}0]$ direction on the surface of (Ga,Mn)As layers grown on GaAs(001) substrates and buffer layers, with periodicity of about 50 nm in all samples that have been studied. These samples show the strong symmetry breaking uniaxial magneticanisotropy normally observed in such materials. We observe a clear correlation between the amplitude of the surface ripples and the strength of the uniaxial magneticanisotropy component suggesting that these ripples might be the source of such anisotropy.

Very high magneticfield annealing is shown to affect the magneticanisotropy in FeCo-base nanocrystalline soft ferromagnetic alloys. Alloys of composition Fe(44.5)Co(44.5)Zr(7)B(4) were prepared by melt spinning into amorphous ribbons, then wound to form toroidal bobbin cores. One set of cores was crystallized in a zero field at 600 deg. C for 1 h, then, field annealed at 17 tesla (T) at 480 deg. C for 1 h. Another set was crystallized in a 17-T field at 480 deg. C for 1 h. Field orientation was transverse to the magnetic path of the toroidal cores. An induced anisotropy is indicated by a sheared hysteresis loop. Sensitive torque magnetometry measurements with a Si cantilever sensor indicated a strong, uniaxial, longitudinal easy axis in the zero-field-crystallized sample. The source is most likely magnetoelastic anisotropy, caused by the residual stress from nanocrystallization and the nonzero magnetostriction coefficient for this material. The magnetostrictive coefficient lambda(5) is measured to be 36 ppm by a strain gage technique. Field annealing reduces the magnitude of the induced anisotropy. Core loss measurements were made in the zero-field-crystallized, zero-field-crystallized- than-field-annealed, and field-crystallized states. Core loss is reduced 30%-50% (depending on frequency) by field annealing. X-ray diffraction reveals no evidence of crystalline texture or orientation that would cause the induced anisotropy. Diffusional pair ordering is thought to be the cause of the induced anisotropy. However, reannealing the samples in the absence of a magneticfield at 480 deg. C does not completely remove the induced anisotropy.

An outstanding problem in nano-magnetism is to stabilize the magnetic order in nanoparticles at room temperatures. For ordinary ferromagnetic materials, reduction in size leads to a decrease in the magneticanisotropy resulting in superparamagnetic relaxations at nanoscopic sizes. In this work, we demonstrate that using wet chemical synthesis, it is possible to stabilize cobalt carbide nanoparticles which have blocking temperatures exceeding 570 K even for particles with magnetic domains of 8 nm. First principles theoretical investigations show that the observed behavior is rooted in the giant magnetocrystalline anisotropies due to controlled mixing between C p- and Co d-states.

The thermal stability of pinned synthetic ferrimagnets with perpendicular anisotropy is investigated. These structures consist of two [Pt/Co] mutilayers (MLs) antiferromagnetically coupled through a Ru spacer, in which one of them is, in turn, exchange biased with FeMn. The switching fields of both MLs can be tuned, at a given temperature, by varying the relative number of (Pt/Co) repeats comprised in each ML. These fields are determined by the values of the exchange constant through the Ru, ARu, and the exchange constant with FeMn, Apinning. Interestingly, for some compositions, it is found that the order in which the two MLs switch during magnetization reversal changes depending on temperature. This effect is due to the different thermal evolution of ARu and Apinning.

The origin of the magneticanisotropy in a very disordered Fe-Si alloy has been investigated. The alloy containing 40 percent at. Si was prepared in the form of a thin film in a DC magnetron sputtering chamber. Structural disorder was obtained from Extended X-ray Absorption Fine Structure spectroscopy. The uniformity and lack of inhomogeneities at a microscopic level was checked by measuring their transverse magnetic susceptibility and hysteresis loops. The orbital component of the magnetic moment was measured by X-ray Magnetic Circular Dichroism spectroscopy. The orbital moment was extraordinary high, 0.4mB. Such a high value contrasted with the relatively small uniaxial anisotropy energy of the thin film (2kJ/m3). This suggests that the cause of the magneticanisotropy in this alloy was a small degree of correlation in the orientation of the local orbital moments along a preferential direction.

W-band (? ? 94 GHz) electron paramagnetic resonance (EPR) spectroscopy was used for a single-crystal study of a star-shaped Fe3Cr single-molecule magnet (SMM) with crystallographically imposed trigonal symmetry. The high resolution and sensitivity accessible with W-band EPR allowed us to determine accurately the axial zero-field splitting terms for the ground (S = 6) and first two excited states (S = 5 and S = 4). Furthermore, spectra recorded by applying the magneticfield perpendicular to the trigonal axis showed a ?/6 angular modulation. This behavior is a signature of the presence of trigonal transverse magneticanisotropy terms whose values had not been spectroscopically determined in any SMM prior to this work. Such in-plane anisotropy could only be justified by dropping the so-called giant spin approach and by considering a complete multispin approach. From a detailed analysis of experimental data with the two models, it emerged that the observed trigonal anisotropy directly reflects the structural features of the cluster, i.e., the relative orientation of single-ion anisotropy tensors and the angular modulation of single-ion anisotropy components in the hard plane of the cluster. Finally, since high-order transverse anisotropy is pivotal in determining the spin dynamics in the quantum tunneling regime, we have compared the angular dependence of the tunnel splitting predicted by the two models upon application of a transverse field (Berry-phase interference).

In Mn3O4, the magnetization along the c axis is different from that along the ab plane even in the strong field of 30 T. To investigate the origin of the huge magneticanisotropy, Mn2+ and Mn3+ nuclear magnetic resonance spectra were measured in the 7-T magneticfield. The canting angle of the magnetic moments was estimated for various directions of field by rotating a single-crystalline Mn3O4 sample. One of the main results is that Mn3+ moments lie nearly in the ab plane in the external field perpendicular to the plane, meaning that the macroscopic magneticanisotropy of Mn3O4 originates from the magneticanisotropy of Mn3+ in the ab plane. The anisotropyfield is estimated to be about 65 T. It is obvious that the Yafet-Kittel structure made of Mn2+ and Mn3+ spins lies in the ab plane due to this huge magneticanisotropy, contrary to the previous reports. By the least-squares fit of the canting angle data for various field directions to a simple model, we obtained that JBB=1.88JAB-0.09 meV and KA=-14.7JAB+2.0 meV, where JAB, JBB, and KA are the exchange interaction constants between Mn2+ moments, Mn2+ and Mn3+ moments, and an anisotropy constant of Mn2+, respectively.

Time resolved magneto-optical Kerr measurements are carried out to study the precessional dynamics of ferromagnetic thin films with out-of-plane anisotropy. A combined analysis of parameters, such as coercive fields, magneticanisotropy, and Gilbert damping ?, is reported. Using a macrospin approximation and the Landau-Lifshitz-Gilbert equation, the effective anisotropy and ? are obtained. A large damping varying with the applied field as well as with the thickness of the ferromagnetic layer is reported. Simulations using a distribution in the effective anisotropy allow us to reproduce the field evolution of ?. Moreover, its thickness dependence correlates with the spin pumping effect.

Linear magnetoresistance (MR) is an important attribute for magnetic sensor designs for space applications, three dimensional detection of the magneticfield, and high field measurements. Here we demonstrate that a large linear MR of up to 22% can be achieved in a magnetic tunnel junction that consists of two ferromagnetic layers, one with out of plane and one with in plane magneticanisotropy. The tunnelling magnetoresistance (TMR) is measured with the electrical current perpendicular to the film plane. The magnetic configuration of the device is analyzed.

The induced uniaxial anisotropy constant, Ku, and the saturation magnetization, Ms, in 80-Permalloy films were examined as a function of thickness by a method involving the magnetoresisttance effect. The films were evaporated in a magneticfield. In contrast to Ms which was independent of thickness, Ku decreased continuosly with decreasing thickness and vanished around 100 Å. The value of Ku,

In order to further increase the recording density in hard disk drives, new media materials are required. Two essential parameters of future recording media are a large uniaxial magneticanisotropy energy (MAE) Ku and a large saturation magnetization Ms. Based on first-principles theory, we predict that very specific structural distortions of FeCo alloys possess these desired properties. The discovered alloy

We derive an upper limit of B{sub 0}{lt}3.4{times}10{sup -9}({Omega}{sub 0}h{sup 2}{sub 50}){sup 1/2} G on the present strength of any primordial homogeneous magneticfield. The microwave background anisotropy created by cosmological magneticfields is calculated in the most general flat and open anisotropic cosmologies containing expansion-rate and 3-curvature anisotropies. Our limit is derived from a statistical analysis of the 4-year Cosmic Background Explorer (COBE) data for anisotropy patterns characteristic of homogeneous anisotropy averaged over all possible sky orientations with respect to the COBE receiver. The limits we obtain on homogeneous magneticfields are stronger than those imposed by nucleosynthesis. {copyright} {ital 1997} {ital The American Physical Society}

A set of equations describing the motion of a free magnetic nanoparticle in an external magneticfield in a vacuum, or in a medium with negligibly small friction forces is postulated. The conservation of the total particle momentum, i.e. the sum of the mechanical and the total spin momentum of the nanoparticle is taken into account explicitly. It is shown that for the motion of a nanoparticle in uniform magneticfield there are three different modes of precession of the unit magnetization vector and the director that is parallel the particle easy anisotropy axis. These modes differ significantly in the precession frequency. For the high-frequency mode the director points approximately along the external magneticfield, whereas the frequency and the characteristic relaxation time of the precession of the unit magnetization vector are close to the corresponding values for conventional ferromagnetic resonance. On the other hand, for the low-frequency modes the unit magnetization vector and the director are nearly parallel and rotate in unison around the external magneticfield. The characteristic relaxation time for the low-frequency modes is remarkably long. This means that in a rare assembly of magnetic nanoparticles there is a possibility of additional resonant absorption of the energy of alternating magneticfield at a frequency that is much smaller compared to conventional ferromagnetic resonance frequency. The scattering of a beam of magnetic nanoparticles in a vacuum in a non-uniform external magneticfield is also considered taking into account the precession of the unit magnetization vector and director.

Much of the physics of condensed matter reflects electron-electron correlations. On an independent-electron level, correlations are described by a single Slater determinant with broken spin symmetry. This approach includes Hund's rule correlations as well the LSDA and LSDA+U approximations to density-functional theory (DFT). However, from Kondo and heavy-fermion systems it is known that the independent-electron approach fails to describe spin-charge separation in strongly correlated systems, necessitating the use of two or more Slater determinants. Using first-principle and model calculations, we show that spin-charge separation strongly affects the leading rare-earth anisotropy contribution in top-end permanent magnet materials such as Nd2Fe14B and SmCo5. Explicit correlation results are obtained for two limiting cases. First, we derive the density functional for tripositive rare-earth ions in a Bethe-type crystal field. The potential looks very different from the LSDA(+U) potentials, including gradient corrections. Second, we use a simple model to show that Kondo-type spin-charge separation yield a rare-earth anisotropy contribution absent in the independent-electron approach. This research is supported by DOE (DE-FG02-04ER46152).

The influences of uniaxial in-plane anisotropy on the properties of ordered magnetic structures generated by the DM interaction were investigated by performing Monte-Carlo simulated annealing. The uniaxial anisotropy aligns the magnetic structure along a specific direction and helps to organize magnetic skyrmions to form either a horizontal or a vertical hexagonal structure, depending on the anisotropy strength. The uniaxial in-plane anisotropy not only enhances the ordering of the structure but also enriches the phases of the system, which include a rectangular lattice structure of skyrmions and 1D skyrmion arrays separated by stripe domains. We investigate the formation conditions of the anisotropy strength and the external field for various magnetic phases.

Large magneticanisotropy and coercivity are key properties of functional magnetic materials and are generally associated with rare earth elements. Here we show an extreme, uniaxial magneticanisotropy and the emergence of magnetic hysteresis in Li?(Li(1-x)Fe(x))N. An extrapolated, magneticanisotropyfield of 220?T and a coercivity field of over 11?T at 2?K outperform all known hard ferromagnets and single-molecular magnets. Steps in the hysteresis loops and relaxation phenomena in striking similarity to single-molecular magnets are particularly pronounced for x?1 and indicate the presence of nanoscale magnetic centres. Quantum tunnelling, in the form of temperature-independent relaxation and coercivity, deviation from Arrhenius behaviour and blocking of the relaxation, dominates the magnetic properties up to 10?K. The simple crystal structure, the availability of large single crystals and the ability to vary the Fe concentration make Li?(Li(1-x)Fe(x))N an ideal model system to study macroscopic quantum effects at elevated temperatures and also a basis for novel functional magnetic materials. PMID:24566374

The continued progress of modern information technology relies on understanding the infuence of magneticanisotropy on magnetic thin fims. In this work, two sources of magneticanisotropy are examined in two different soft ferromagnets: a uniaxial anisotropy induced during the fabrication of Ni80Fe 20 and exchange anisotropy, or exchange bias, which occurs at the interface of Ni77Fe14Cu5Mo4/Fe50Mn 50 bilayer. A home-built Magneto-optical Kerr effect magnetometer is used to measure the magnetic response of the soft ferromagnetic films and details of its construction are also discussed. A simple model of uniaxial anisotropy is described, then applied, to the uniaxial NiFe film and deviations from the model are critically analyzed. The exchange bias and coercive fields of NiFeCuMo/FeMn are reported for the first time and studied as a function of buffer layer material. The influence of the different buffer layer materials on the magnetization response of the bilayer is explained from a structural standpoint.

High-spin paramagnetic manganese defects in polar piezoelectric zinc oxide exhibit a simple, almost axial anisotropy and phase coherence times of the order of a millisecond at low temperatures. The anisotropy energy is tunable using an externally applied electric field. This can be used to control electrically the phase of spin superpositions and to drive spin transitions with resonant microwave electric fields. PMID:23383938

We have fabricated oxide-based spin-filter junctions in which we demonstrate that magneticanisotropy can be used to tune the transport behavior of spin-filter junctions. We have demonstrated spin-filtering behavior in La0.7Sr0.3MnO3/CoCr2O4/Fe3O4 and La0.7Sr0.3MnO3/MnCr2O4/Fe3O4 junctions where the interface anisotropy plays a significant role in determining transport behavior. Detailed studies of chemical and magnetic structure at the interfaces indicate that abrupt changes in magneticanisotropy across the nonisostructural interface is the cause of the significant suppression of junction magnetoresistance in junctions with MnCr2O4 barrier layers.

We report an approach to altering the magnetic properties of (111) textured Co/Pt multilayer films grown on sapphire (0001) substrates in a controlled way using single-pulse laser irradiation. The as-grown films reveal a strong perpendicular magneticanisotropy induced by interfacial anisotropy. We show that laser irradiation can chemically mix the multilayer structure particularly at the interfaces, hence reducing the perpendicular magneticanisotropy and coercivity in a controlled manner depending on laser fluence. As a result, perpendicular films can also be magnetically patterned into hard and soft magnetic regions using a regular two-dimensional lattice of polystyrene particles acting as an array of microlenses.

Spin-polarized currents represent an efficient tool for manipulating ferromagnetic nanostructures but the critical current density necessary for the magnetization switching is usually too high for applications. Here we show theoretically that, in magnetic tunnel junctions having electric-field-dependent interfacial anisotropy, the critical density may reduce down to a very low level (~104?A cm?2) when the junction combines small conductance with the proximity of free layer to a size-driven spin reorientation transition. The theory explains easy magnetization switching recently discovered in CoFeB/MgO/CoFeB tunnel junctions, surprisingly showing that it happens when the spin-transfer torque is relatively small, and provides a recipe for the fabrication of magnetic tunnel junctions suitable for industrial memory applications. PMID:24067783

Magnetization and electrical resistivity measurements have been performed on a stoichiometric single crystalline magnetite Fe3O4 thin film (thickness of ca. 500nm) MBE deposited on MgO (100) substrate. The aim of these studies was to check the influence of preparation method and sample form (bulk vs. thin film) on magneticanisotropy properties in magnetite. The film magnetization along ?001? versus applied

Very high magneticfield annealing is shown to affect the magneticanisotropy in FeCo-base nanocrystalline soft ferromagnetic alloys. Alloys of composition Fe44.5Co44.5Zr7B4 were prepared by melt spinning into amorphous ribbons, then wound to form toroidal bobbin cores. One set of cores was crystallized in a zero field at 600°C for 1 h, then, field annealed at 17 tesla (T) at

We conducted a rock magnetic, magneticanisotropy and paleomagnetic study of the brecciated LL6 bensour meteorite a few months after its fall on Earth. Magnetic properties, in particular hysteresis loops before and after heating, as well as high fieldanisotropy indicate that tetrataenite is the major magnetic mineral. A very strong coherent susceptibility and remanence anisotropy is evidenced and interpreted as due to the last large impact responsible for the post-metamorphic and post-brecciation compaction of this material. Demagnetization of mutually oriented sub-samples evidences three components of magnetization. Medium and high coercivity components carried by tetrataenite are randomly distributed down to a scale of 0.1 cc. They represent the magnetization acquired by tetrataenite during its formation by low-temperature atomic ordering of taenite, but the link with the original magnetization of taenite and kamacite grains, acquired during cooling of the parent body after metamorphism, is unknown. Alternatively this randomness may be due to a post-metamorphic thermoremanent magnetization subsequently randomized by brecciation. A non random low-coercivity component is also evidenced. We show that it clearly predates the fall of the meteorite on Earth and postdates the last major impact on the meteorite parent body. The coercivity spectrum of this component as well as the close relation with the impact-related petrofabric indicate that the low coercivity component is likely related to this major impact, possibly in quasi-absence of ambient magneticfield.

Experimental investigations of deformation-induced remagnetization demonstrate that a primary remanence can survive conditions equivalent to moderate metamorphism in certain cases and that pre-deformation magnetic fabric can play an important role in determining the remanence stability. Results from shear experiments at elevated temperatures on magnetite-bearing rock-analogues demonstrate that complex interactions between temperature, applied field, stress, and anisotropy are responsible for determining the robustness of a pre-deformation magnetization. Syndeformational remagnetization is partly attributed to a stress-softening mechanism resulting in a piezoremanent magnetization, but the extent of remagnetization was largely dependent on the initial anisotropy, and generally unrelated to the deformation fabric. Similarly, the initial anisotropy of deformed samples is found to strongly influence the development of deformation fabrics and overprinting causes the deformation geometry to be obscured at low strains. These results raise several questions concerning paleomagnetic study in tectonized terranes and highlight a research area with much potential for future study.

Half-metallic Co-based full-Heusler alloys with perpendicular magneticanisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3?nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropyfield of ~8.0?kOe can be achieved at PO2?=?12% for the sample of tCFAO?=?2.1?nm or at PO2?=?7% for tCFAO?=?2.8?nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices. PMID:26190066

High-anisotropy MnBi nanostructures have been fabricated by in-situ annealing of Bi/Mn/Bi multilayers and magnetic-field annealing of melt-spun MnxBi100-x ribbons. The ratio of Mn to Bi affects the concentration of NiAs-type MnBi, the degree of c-axis orientation, and phase distribution. For x = 50, the MnxBi100-x film exhibits the optimum nanostructure in which MnBi grains are uniformly separated by a thin layer of Bi. This has produced a record value of (BH)max = 16.3 MGOe for this compound. A good c-axis texture has been developed for Mn50Bi50 ribbons with a remanence ratio of 0.94 after magnetic-field annealing and this result subsequently leads to (BH)max = 9.2 MGOe, the highest value for bulk MnBi materials. The reason for the much higher energy product for the Mn50Bi50 film compared to the Mn50Bi50 ribbon is that the ribbon has a comparatively lower coercivity induced by inhomogeneous distribution of intergranular Bi. The effect of element doping, optimization of preparation parameters, and temperature dependence of properties also will be discussed. This work was supported by US DOE/BES (DE-FG2-04ER46152) and NCMN.

Strong spin-orbit coupling is a pre-requisite for hard magnetism with high coercive magneticfields. Magnetic oxides containing 5d ions such as Ir4+ should show significant spin-orbit coupling due to the high Z value. Furthermore, in 5d ions, the comparable energy scales of crystal-electric field splitting, Coulomb repulsion and spin-orbit interactions create unusual electronic ground states that can entangle spins and orbits, mix t2g and eg levels and drive magnetic exchange anisotropy. Another set of interesting electronic ground states can arise when 5d orbitals overlap 3d orbitals. In the compound Sr3NiIrO6, electronic structure calculations predict that the 3d orbitals of the Ni2+ ion directly overlap 5d orbitals of the Ir4+ ion. In addition to a ``Jeff = 1/2'' Ir4+ ground state that mixes t2g and eg levels, the Ni2+ should show strong single-ion anisotropy [1-3]. We present magnetization measurements of Sr3NiIrO6 to high magneticfields. We demonstrate magnetic hysteresis with a record 55 Tesla coercive magneticfield and long stability over time in some crystals. More generally, the A3BB'O6 family of compounds shows hard magnetism as B' ion goes from 3d to 4d to 5d. Further complexities to do with evolving magnetic order and magnetic frustration also present in this family.

A magneticfield sensor that isotropically senses an incident magneticfield. This is preferably accomplished by providing a magneticfield sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magneticfield. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magneticfield sensor device provides an output that is relatively independent of the direction of the incident magneticfield in the sensor plane.

Growth of single crystals of (Fe1-xCox)2B (0 <= x <= 1) and detailed characterization of their magnetic properties will be presented. Despite the fact that both Fe2B and Co2B show a planar anisotropy at room temperature, we observe a uniaxial anisotropy at intermediate doping which makes (Fe,Co)2B a promising system for permanent magnet applications in a system without rare-earth element. Comparison with recent band structure calculations will be presented. The temperature dependence of the anisotropy measured on single crystals from 2 K to 1000 K shows some unusual variations with an increase of the magneticanisotropy with increasing temperature at some specific substitution. This work is supported by the Critical Materials Institute, an Energy Innovation Hub funded by the US DOE and by the Office of Basic Energy Science, Division of Materials Science and Engineering. Ames Laboratory is operated for the US DOE by Iowa State University under Contract No. DE-AC02-07CH11358.

The microstructure and magnetic properties of Nd-Fe-B films with thicknesses from 100 nm to 3 nm have been investigated. All the films show excellent perpendicular magneticanisotropy with a squareness ratio of 1 in the perpendicular direction and almost zero coercivity in the in-plane direction. Of particular interest is that the initial magnetization curves sensitively depended on the film thickness. Films thicker than 15 nm show steep initial magnetization curve. Although the films have coercivities larger than 21 kOe, the films can be fully magnetized from the thermally demagnetized state with a field as small as 5 kOe. With the decrease of film thickness to 5 nm, the initial magnetization curve becomes flat. The evolution of initial magnetization curves with film thickness can be understood by the microstructure of the films. Films with thickness of 15 nm show close-packed grains without any intergranular phases. Such microstructures lead to steep initial magnetization curves. On the other hand, when the film thickness decreased to 3 nm, the film thickness became nonuniform. Such microstructure leads to flat initial magnetization curves.

An analysis of the magnetoelastic coupling and the magnetocrystalline anisotropy in rare earth intermetallic compounds has been undertaken on the basis of a microscopic description. Crystal electric field and exchange interaction have been considered as the main contribution to the free energy in order to explain the behaviour. Magnetostriction measurements on cubic (RAl 2, RNi 2) and uniaxial (RCo 5 and R 2Fe 14B) compounds are reported. A single ion origin for the magnetocristalline anisotropy of the R 3+ ion has been tested, which has allowed a complete and reliable description of the spin reorientation processes because of the interplay of competing anisotropies.

The evidence of cosmic magnetism is examined, taking into account the Zeeman effect, beats in atomic transitions, the Hanle effect, Faraday rotation, gyro-lines, and the strength and scale of magneticfields in astrophysics. The origin of magneticfields is considered along with dynamos, the conditions for magneticfield generation, the topology of flows, magneticfields in stationary flows, kinematic turbulent

The magnetic properties of FePt thin films have been modified by exposing the samples to irradiation of 4 MeV Cl{sup 2+} ions. Patterned magnetic films, without modified topographical profile, were fabricated by irradiating the films through a shadowing micrometric mask. The structural changes, ascribed to the ion-beam-induced amorphization of the thin films, promote the modification of the magneticanisotropy. In particular, the out-of-plane component of the magnetization decreases simultaneously with an enhancement of in-plane anisotropy by increasing ion fluence. Moreover, the nonirradiated regions present unexpected anisotropic behavior owing to the stray field of the irradiated regions. The control of this effect, which can have unwished consequences for the patterning of magnetic properties by ion bombardment, needs to be suitably addressed.

The calculation of high frequency complex permeability of thin ferromagnetic film requires the measured values of its saturation magnetization, anisotropic magneticfield intensity, resistivity, and thickness. It is often observed that the calculated permeability using the Landau-Lifshitz-Gilbert (LLG) theory does not agree well with the measured permeability of thin film with in-plane uniaxial magneticanisotropy, owing to the measured anisotropic magneticfield intensity, saturation magnetization, etc., are not effective values at high frequency. In this work, the Landau-Lifshitz ferromagnetic resonance model is modified to take the skin depth effect into consideration. In the comparison study, its calculated magnetic permeability curves (real and imaginary) agrees very well with those calculated from the LLG model. In addition, an algorithm process to extract effective magnetic parameters (saturation magnetization Ms, magneticanisotropyfield Ha, and damping factor ?) has been developed. The algorithm process has been tested for the reported magnetic permeability curves of two magnetic films (Si/NiFe/FeCoB and CoZrRe). The extracted parameters are well agreed with those reported. It is also reported that the consideration of skin depth effect is necessary for samples with lower electrical resistivity.

We present a study of granular Co-Pt multilayers by means of high-resolution transmission electron microscopy (HRTEM), extended x-ray absorption fine structure (EXAFS), SQUID-based magnetic measurements, anomalous Hall effect (AHE), and x-ray magnetic circular dichroism (XMCD). We describe these granular films as composed of particles with a pure cobalt core surrounded by an alloyed Co-Pt interface, embedded in a Pt matrix. The alloy between the Co and Pt in these granular films, prepared by room temperature sputter deposition, results from interdiffusion of the atoms. The presence of this alloy gives rise to a high perpendicular magneticanisotropy (PMA) in the granular films, as consequence of the anisotropy of the orbital moment in the Co atoms in the alloy, and comparable to that of highly-ordered CoPt L 10 alloy films. Their magnetic properties are those of ferromagnetically coupled particles, whose coupling is strongly temperature dependent: at low temperatures, the granular sample is ferromagnetic with a high coercive field; at intermediate temperatures the granular film behaves as an amorphous asperomagnet, with a coupling between the grains mediated by the polarized Pt, and at high temperatures, the sample has a superparamagnetic behavior. The coupling/decoupling between the grains in our Co-Pt granular films can be tailored by variation of the amount of Pt in the samples.

A new surface sensor probe comprising an angular array of Hall effect sensors has been developed for characterization of residual stresses in ferrous materials by means of stress-induced magneticanisotropy measurements. The sensor probe applies a radially spreading ac magneticfield to a test sample, and detects stray fields in different directions simultaneously to determine the principal stress axes. In

A new surface sensor probe comprising an angular array of Hall effect sensors has been developed for characterization of residual stresses in ferrous materials by means of stress-induced magneticanisotropy measurements. The sensor probe applies a radially spreading ac magneticfield to a test sample, and detects stray fields in different directions simultaneously to determine the principal stress axes. In

Ten-fold-like magneticanisotropy is reproducibly observed in electrical conductivity of Al71Pd21Mn8 icosahedral quasicrystal. The voltage V is measured, where the current I is along a five-fold axis of the sample and is perpendicular to the magneticfield H. The voltage difference ?V=V(+I)+V(?I) has angle dependences at H=30?80 kOe and the temperature T=2?8 K. ?V is about 3000 times smaller than

Measurement of the anisotropy dispersion using ferromagnetic resonance at radio frequencies has been reconsidered, taking into account the skin effect in relatively thick soft magnetic films. Numerical calculations for 1 ¿m thick amorphous films showed that eddy current losses are comparable to the resonance absorption. The measured absorption for CoZr film is larger than the calculated absorption under a low

Controlling and designing quantum magnetic properties by an external electric field is a key challenge in modern magnetic physics. Here, from first principles, the effects of an external electric field on the magnetocrystalline anisotropy (MCA) in ferromagnetic transition-metal monolayers are demonstrated which show that the MCA in an Fe(001) monolayer [but not in Co(001) and Ni(001) monolayers] can be controlled

Correlated particle and magneticfield measurements by the ISEE 3 spacecraft are presented for the loop structure behind the interplanetary traveling shock event of Nov. 12, 1978. Following the passage of the turbulent shock region, strong bidirectional streaming of low-energy protons is observed for approximately 6 hours, corresponding to a loop thickness of about 0.07 AU. This region is also characterized by a low relative variance of the magneticfield, a depressed proton intensity, and a reduction in the magnetic power spectral density. Using quasi-linear theory applied to a slab model, a value of 3 AU is derived for the mean free path during the passage of the closed loop. It is inferred from this observation that the proton regime associated with the loop structure is experiencing scatter-free transport and that either the length of the loop is approximately 3 AU between the sun and the earth or else the protons are being reflected at both ends of a smaller loop.

We have fabricated epitaxial single crystalline cobalt ferrite (CoFe2O4) thin films on CoCr2O4 buffered SrTiO3 and MgAl2O4 substrates. Structural characterization by X-ray diffraction, Rutherford backscattering spectroscopy and atomic force microscopy indicates excellent crystallinity. Magneticanisotropy measurements in the in-plane and perpendicular directions as a function of film thickness provide strong evidence for the dominant role of strain in the magnetic

Magneticanisotropy of compounds of CrSb, (Cr0.9Mn0.1)Sb and (Cr0.8Mn0.2)Sb was investigated by using their single crystals. From the measurements of torque curves by means of torsion pendulum magnetometer, the difference between the susceptibilities parallel and perpendicular to the c-axis of the hexagonal crystal lattice was obtained for each specimen. It was confirmed that the magnetic spin axis lies along the

In this activity, learners explore the magneticfield of a bar magnet as an introduction to understanding Earth's magneticfield. First, learners explore and play with magnets and compasses. Then, learners trace the field lines of the magnet using the compass on a large piece of paper. This activity will also demonstrate why prominences are always "loops."

Single-crystal torque magnetometry performed on weakly-coupled polynuclear systems provides access to a complete description of single-site anisotropy tensors. Variable-temperature, variable-field torque magnetometry was used to investigate triiron(III) complex [Fe3La(tea)2(dpm)6] (Fe3La), a lanthanum(III)-centred variant of tetrairon(III) single molecule magnets (Fe4) (H3tea = triethanolamine, Hdpm = dipivaloylmethane). Due to the presence of the diamagnetic lanthanoid, magnetic interactions among iron(III) ions (si = 5/2) are very weak (<0.1 cm(?1)) and the magnetic response of Fe3La is predominantly determined by single-site anisotropies. The local anisotropy tensors were found to have Di > 0 and to be quasi-axial with |Ei/Di| ~ 0.05. Their hard axes form an angle of approximately 70° with the threefold molecular axis, which therefore corresponds to an easy magnetic direction for the molecule. The resulting picture was supported by a High Frequency EPR investigation and by DFT calculations. Our study confirms that the array of peripheral iron(III) centres provides substantially noncollinear anisotropy contributions to the ground state of Fe4 complexes, which are of current interest in molecular magnetism and spintronics. PMID:25014192

The interface magnetocrystalline anisotropy energy (MAE) in Fe/CeH2 multilayers has been site and element-specifically isolated by combining soft x-ray resonant magnetic scattering (SXRMS) with soft x-ray standing waves. Using the different temperature evolutions of the Fe and Ce SXRMS contributions, following an in-plane to out-of-plane spin reorientation, the interface Fe 3d MAE and Ce 4f single-ion anisotropy have been separated. The results demonstrate that the transition metal interface MAE dominates the spin reorientation while the rare-earth contribution becomes significant only at much lower temperatures.

We have deposited self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) thin films on Pb(Mg1\\/3Nb2\\/3)0.7Ti0.3O3 (PMN-PT) substrates and studied the change in magneticanisotropy under different strain conditions induced by an applied electric field. After electric field poling, we observed (i) giant magnetization change: magnetization of original CFO phase is three times larger than that of strained one and (ii) magnetic force microscopy line

Increasing electrification brings increased human exposures to electric and magneticfields, commonly called EMFs, and growing evidence suggests that exposure to even low frequency, low energy, electric and magneticfields may be related to adverse health effects. This paper focuses on magneticfields and strategies that address them. The challenges faced by scientists in understanding magneticfield interactions with humans,

The formation of nanoparticle assemblies in nature is characteristic for magnetotactic bacteria (MTB), where magnetite (Fe3O4) nanocrystals are formed intracellularly. The nanocrystals are usually aligned along their [111] axis and are held in chain configuration by a skeletal filament. This alignment, with [111] being the magnetization easy axis of magnetite, generates a strong interaction-induced dipole field along the cellular body axes, which gives rise to a distinct uniaxial anisotropy. The anisotropy properties of MTB are readily detectable by ferromagnetic resonance spectroscopy (FMR), where spectra of randomly oriented MTB show characteristic features with two low-field peaks and a strong high-field minimum. The anisotropy properties of such chain assemblies of nanocrystals are examined in detail by approximating the chain as a single ellipsoid. In this approximation both the cubic magnetocrystalline anisotropyfield (Hcub) and the effective uniaxial field (Huni) are considered, and used to simulate FMR spectra [1]. By varying the two parameters Huni and Hcub we can simulate signals that fit the experimental FMR spectra obtained from cultured intact MTB, thus easily extracting the anisotropyfields in the samples. We find that this method can be used with good precision to model the behavior of MTB quantitatively. Moreover, this method is applied to investigate the evolution of the magneticanisotropy in a growth series of MTB under laboratory conditions. Special focus is given on the superparamagnetic effects due to small particle sizes in the initial growth stages. The effective uniaxiality in MTB, which is essential for magnetotaxis, is evident after the cubic anisotropyfield is strong enough to hold the magnetic moments along the [111] direction of the crystallites [2]. The quantitative analysis of anisotropy traits in intact cultured MTB could be valuable for the detection of MTB in geological systems that can contribute to a better insight into microbial ecology during Earth's history. References: [1] M. Charilaou, M. Winklhofer, A. U. Gehring, J. Appl. Phys. 109, 093903 (2011). [2] M. Charilaou, K. K. Sahu, D. Faivre, A. Fischer, I. García-Rubio, A. U. Gehring, Appl. Phys. Lett. 99, 182504 (2011).

We have investigated the exchange coupling between a bottom FePt thin film layer capped with different Mn-oxides. Results have shown that the magnetization reversal of the soft FePt layer is influenced strongly by the capped Mn-oxide layer (Mn, MnO, and Mn3O4), as revealed by the enhanced coercivities. Typical temperature dependent magnetization between zero-field cooled (ZFC) and field cooled (FC) scans was observed in the Mn-oxide (8%O2/Ar)/FePt bilayer that exhibited a blocking temperature (TB  120 K) close to the Nèel temperature, TN, of MnO. However, the Mn/FePt bilayer exhibited unusual temperature dependent of M vs. T, implying that intermixing between Mn and FePt interfaces formed an AF FeMn that may have enabled a high irreversibility temperature (Tirr.  400 K) compared to almost identical ZFC and FC curves from weaker exchange coupling between FePt and the Mn3O4 created with 21 and 30%O2/Ar deposition conditions.

A magnetoresistive (MR) read sensor design for magnetic recording has been proposed in an attempt to solve the magnetization distribution and thermal stability problems of nanometer-scale read sensors. In this design, the free layer has a perpendicular-to-plane easy axis and the reference layer has an in-plane easy axis. The giant-magnetoresistive film with this structure is demonstrated in which the free layer is a [CoFe/Pt]n multilayer. The structure of the [CoFe/Pt]n multilayer has to be optimized so that the magnetic properties of the free layer can meet the requirements of a MR read head.

By exploiting density-matrix renormalization group techniques, we investigate the spin dynamics of a spin-1/2 one-dimensional J1-J2 XXZ model with competing ferromagnetic J1 and antiferromagnetic J2 exchange couplings under applied magneticfields. Numerical results of spin excitation spectra show that in the field-induced spin quadrupole regime, the longitudinal component has a gapless mode and the transverse component has a gapped mode irrespective of the exchange anisotropy. The excitation gap of the transverse spin excitation increases as the exchange anisotropy increases over the XY-like and Ising-like regions, demonstrating that two-magnon bound states are stabilized due to the easy-axis anisotropy.

Electronic configurations and magneticanisotropy of organometallic metallocenes (MCp2s) were investigated by means of first principles calculations based on the constraint density functional theory. The results predict that the ground states for M = Cr, Mn, Fe, Co, and Ni are the 3E2 g, 2E2 g, 1A1 g, 2E1 g, and 3A2 g states, respectively. The magnetizations of the CoCp2 and NiCp2 energetically favor highly orienting along the perpendicular and parallel directions to the cyclopentadienyl (Cp) plane, respectively, and the others show almost no preference for the magnetic easy axis.

This lesson introduces students to the effects of magneticfields in matter addressing permanent magnets, diamagnetism, paramagnetism, ferromagnetism, and magnetization. First students must compare the magneticfield of a solenoid to the magneticfield of a permanent magnet. Students then learn the response of diamagnetic, paramagnetic, and ferromagnetic material to a magneticfield. Now aware of the mechanism causing a solid to respond to a field, students learn how to measure the response by looking at the net magnetic moment per unit volume of the material.

In this activity, students investigate the presence of magneticfields around magnets, the sun and the earth. They will explore magneticfield lines, understand that magnetic lines of force show the strength and direction of magneticfields, determine how field lines interact between attracting and repelling magnetic poles, and discover that the earth and sun have magnetic properties. They will also discover that magnetic force is invisible and that a "field of force" is a region or space in which one object can attract or repel another.

Using ab initio calculations all the components of the magneticanisotropy in a dinuclear [Mn(III)Cu(II)Cl(5-Br-sap)2(MeOH)] single-molecule magnet (SMM) have been computed. These calculations reveal that apart from the single-ion anisotropy, the exchange anisotropy also plays a crucial role in determining the sign as well as the magnitude of the cluster anisotropy. Developed magneto-structural correlations suggest that a large ferromagnetic exchange can in fact reduce the ground-state anisotropy, which is an integral component in the design of SMMs. PMID:24700405

The mechanism of tailored magneticanisotropy in amorphous Co{sub 68}Fe{sub 24}Zr{sub 8} thin films was investigated by ferromagnetic resonance (FMR) on samples deposited without an applied magneticfield, with an out-of-plane field and an in-plane field. Analysis of FMR spectra profiles, high frequency susceptibility calculations, and statistical simulations using a distribution of local uniaxial magneticanisotropy reveal the presence of atomic configurations with local uniaxial anisotropy, of which the direction can be tailored while the magnitude remains at an intrinsically constant value of 3.0(2) kJ/m{sup 3}. The in-plane growth field remarkably sharpens the anisotropy distribution and increases the sample homogeneity. The results benefit designing multilayer spintronic devices based on highly homogeneous amorphous layers with tailored magneticanisotropy.

Patterned hard-soft 2D magnetic lateral composites have been fabricated by e-beam lithography plus dry etching techniques on sputter-deposited NdCo{sub 5} thin films with perpendicular magneticanisotropy. Their magnetic behavior is strongly thickness dependent due to the interplay between out-of-plane anisotropy and magnetostatic energy. Thus, the spatial modulation of thicknesses leads to an exchange coupled system with hard/soft magnetic regions in which rotatable anisotropy of the thicker elements provides an extra tool to design the global magnetic behavior of the patterned lateral composite. Kerr microscopy studies (domain imaging and magneto-optical Kerr effect magnetometry) reveal that the resulting hysteresis loops exhibit a tunable exchange bias-like shift that can be switched on/off by the applied magneticfield.

Achieving 180° magnetization reversal with an electric field rather than a current or magneticfield is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Achieving 180° magnetization reversal with an electric field rather than a current or magneticfield is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Achieving 180° magnetization reversal with an electric field rather than a current or magneticfield is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals.

The magnetic phase diagram of three-dimensional (3D) antiferromagnets with random magneticanisotropy (RMA) is not well understood because systems studied experimentally to date have complicated magnetic structures with competing two-dimensional and three-dimensional exchange interactions. The properties of epitaxial thin films of the 3D RMA antiferromagnet FexNi1-xF2 thin films grown on (110) MgF2 substrates were investigated by magnetometry and neutron scattering. FexNi1-xF2 is an ideal 3D antiferromagnet with which to study this problem due to the single-ion anisotropy energies of the transition metal site which tend to order Ni2+ and Fe2+ spins perpendicular to each other. The magnetic phase diagram determined from these measurements was analyzed using mean field theory. Regions with uniaxial, oblique and easy plane anisotropy were identified. An anisotropy glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs. Supported by the NSF (grant 0903861), the WVHEPC (Research Challenge Grant HEPC.dsr.12.29), the WVU Shared Research Facilities, and the DOE BES.

Because the size of magnetic grains is approaching the superparamagnetic limit in current perpendicular media, it is necessary to produce thin film media made with magnetic alloys with larger magneto-crystalline anisotropy energies to achieve higher recording densities. Due to its high anisotropyfield and good environmental stability, FePt (L10) is the most promising media for achieving such ultra-high recording densities. However, there are several challenges associated with the development of FePt as a perpendicular media. As deposited FePt has disordered fee phase; either high deposition temperature, > 600 oC, or a high temperature post annealing process is required to obtain the ordered L10 structure, which is not desirable for manufacturing purposes. Therefore, techniques that enable ordering at significantly reduced temperatures are critically and urgently needed. Furthermore, in order to use it as a high density recording media, very small (less than 5 nm), uniform and fully-ordered, magnetically isolated FePt (L10) columnar grains with well defined grain boundaries, excellent perpendicular texture and high coercivity are desired. In this study, experiments and research have been mainly focused on the following aspects: (1) controlling of c axis orientation of FePt, (2) obtaining small columnar FePt grains, (3) improving order parameter and magnetic properties at lower ordering temperature. After a systematic experimental investigation, we have found an experimental approach for obtaining highly ordered L1 0 FePt-oxide thin film media at moderate deposition temperatures. In most previous studies, the FePt-Oxide layer is directly deposited on a textured MgO (001) layer. By introducing a double buffer layer in between the FePt-oxide layer and the MgO underlayer, we are able to substantially enhance the L1 0 ordering of the FePt-oxide layer while lowering the deposition temperature to 400oC. The buffer layers also yield a significantly enhanced (001) texture of the formed L10 FePt film. With the order parameter near unity, the coercivity of the resulting granular L10 FePt-oxide film exceeds Hc > 20 kOe with an average grain size about D = 8 nm. With the buffer layer technique, l8kOe coercivity has also been achieved for L10 FePt-oxide film at a grain size of about D = 4.5 nm, but it requires 35% of SiO2 in the magnetic layer. With 9% of Oxide in the film, excellent perpendicular texture, very high order parameter and small grain size of FePt can also be obtained by utilizing RuAl grain size defining layer along with TiN barrier layer. With the Ag buffer layer technique, the microstructure and magnetic properties of FePt films with RuAl grain size defining layer can be further improved.

The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons in water molecules in a host's tissue. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magneticanisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices in which an individual magnetic atom or molecule is coupled to conducting leads. PMID:24317285

This is an activity about magneticfields. Using iron filings, learners will observe magnets in various arrangements to investigate the magneticfield lines of force. This information is then related to magnetic loops on the Sun's surface and the magneticfield of the Earth. This is the second activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

In this activity, students take the age old concept of etch-a-sketch a step further. Using iron filings, students begin visualizing magneticfield lines. To do so, students use a compass to read the direction of the magnet's magneticfield. Then, students observe the behavior of iron filings near that magnet as they rotate the filings about the magnet. Finally, students study the behavior of iron filings suspended in mineral oil which displays the magneticfield in three dimensions.

The current state of the understanding of the magneticfields of galaxies is reviewed. A simple model of the turbulent dynamo is developed which explains the main observational features of the global magneticfields of spiral galaxies. The generation of small-scale chaotic magneticfields in the interstellar medium is also examined. Attention is also given to the role of magnetic

The magneticanisotropy properties of GaMnAs ferromagnetic films have been investigated by using planar Hall effect measurements. The field scan of the planar Hall resistance (PHR) showed a two-step switching behavior indicating a strong cubic anisotropy along the <100> directions. The difference in the behaviors of the PHR for two applied field directions, [ {1bar 10} ] and [110], was understood via the well-known uniaxial anisotropy along the [110] direction. In addition to such known effects, we also found the presence of an asymmetry for the [010] and the [100] directions. This new asymmetry phenomenon was explained by introducing an additional uniaxial anisotropyfield H u2 along the [100] and the [ {bar 100} ] directions, which coincide with the two directions of cubic anisotropy. The values of the anisotropyfields, cubic ( H c ), first uniaxial ( H u1), and second uniaxial ( H u2), were obtained by analyzing the angle dependence of the PHR. Although the value of H u2 is small, its effect is clearly observed at high temperatures above 25 K, where the transition of the magnetization occurred before the field direction had been reversed during the magnetization reversal process.

We present an exactly soluble model of equal spin s1 dimer single molecule magnets. The dimer spins interact via the Heisenberg, Zeeman, and the most general quadratic local and global anisotropic exchange interactions. We derive the Hamiltonian matrix for the general case with each type of anisotropy. For antiferromagnetic couplings and s1 > 1/2, the low temperature T magnetization exhibits a strong influence of single-ion anisotropy. Our results suggest a substantial presence of axial single-ion anisotropy in the s1 = 5/2 Fe2 dimer, [Fe(salen)Cl]2.

The effect of hydrogenation on the magnetic properties of the intermetallic compound ErFe11Ti are studied. Single crystals of the hydrogen-containing compound were obtained. Magnetic characteristics of the ErFe11Ti and ErFe11TiH single crystals have been investigated in the temperature range 4.2750 K and in magneticfields up to 13 kOe. Upon hydrogenation, the uniaxial magneticanisotropy is observed to increase, while

The propagation of linear and nonlinear electrostatic waves is investigated in a magnetized anisotropic electron-positron-ion (e-p-i) plasma with superthermal electrons and positrons. A two-dimensional plasma geometry is assumed. The ions are assumed to be warm and anisotropic due to an external magneticfield. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low (CGL) theory. In the linear regime, two normal modes are predicted, whose characteristics are investigated parametrically, focusing on the effect of superthermality of electrons and positrons, ion pressure anisotropy, positron concentration and magneticfield strength. A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential (disturbance) via a reductive perturbation method. The parametric role of superthermality, positron content, ion pressure anisotropy and magneticfield strength on the characteristics of solitary wave structures is investigated. Following Allen and Rowlands [J. Plasma Phys. 53, 63 (1995)], we have shown that the pulse soliton solution of the ZK equation is unstable to oblique perturbations, and have analytically traced the dependence of the instability growth rate on superthermality and ion pressure anisotropy.

Using the Mossbauer technique we have investigated the electric and magnetic hyperfine interaction in Fe-boracites Fe3B7013X (X = C1, Br, I). The analysis of the Mossbauer spectra below the NBel temperature leads to 3 lattice sites in the case of Fe-CI- and Fe-Br-bora- cite and to at least 4 sites in the Fe-I-boracite, which are different with regard to the

Periodic, finely multilayered thin-film magnetic structures (?200 A?) with high in-plane coercivity suitable for longitudinal recording investigations have been fabricated. CoPt20\\/Pd and CoPt12Cr17\\/Pd periodic multilayers can exhibit a perpendicular orientation, originating from surface anisotropy effects, with a magnitude depending on the thickness of the component layers. The perpendicular orientation influences the transition noise, but for the particular systems studied, the

Magnetic properties of nanocrystalline Ni samples, with average grain sizes, d = 11(1) nm, 19(1) nm and 30(2) nm, synthesized by pulse electrodeposition, have been studied. We observed that (i) at low temperatures, the effective magneto-crystalline anisotropy constant, K1, increases with the crystallite size so as to reach the bulk value at d = 30 nm, and (ii) the rate of thermal decline of K1(T) slows down as the crystallite size reduces.

Spin transfer-related phenomena in nanomagnets have attracted extensive studies. In this paper we shall focus on analysis of individual and combined effects of the external, anisotropy, and demagnetization fields on magnetization dynamics and spin transfer noise. It is found that individual roles of the external, anisotropy, and demagnetization fields, as well as the combined roles of external plus anisotropyfields

To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magneticanisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory. PMID:25597496

The magneto-impedance (MI) profiles of Co 66Fe 4NiB 14Si 15 amorphous ribbons changed sensitively with the annealing temperature, reflecting the change in anisotropyfield, which determines the field dependence of transverse permeability. The effective anisotropyfield, evaluated from these profiles, were discussed in terms of the increase of magnetic softness and microstructural change due to the annealing.

We have fabricated oxide-based spin-filter junctions in which we demonstrate that magneticanisotropy can be used to tune the transport behavior of spin-filter junctions. We have demonstrated spin-filtering behavior in La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/CoCr{sub 2}O{sub 4}/Fe{sub 3}O{sub 4} and La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/MnCr{sub 2}O{sub 4}/Fe{sub 3}O{sub 4} junctions where the interface anisotropy plays a significant role in determining transport behavior. Detailed studies of chemical and magnetic structure at the interfaces indicate that abrupt changes in magneticanisotropy across the nonisostructural interface is the cause of the significant suppression of junction magnetoresistance in junctions with MnCr{sub 2}O{sub 4} barrier layers.

The relationships among magnetic susceptibility anisotropy, finite strain, and progressive deformation have been studied in Permian red shales and slates of the Maritime Alps (southeastern France). These rocks contain deformed reduction spots which serve as finite strain indicators. The magnetic fabric of undeformed regions is modified during deformation to yield characteristic magnetic susceptibility anisotropy patterns and a magnetic equivalent of

Superparamagnetism is a unique feature of magnetic nanoparticles. Spinel ferrite nanoparticles provide great opportunities for studying the mechanism of superparamagnetic properties. CoFe{sub 2}O{sub 4} nanocrystallites have been synthesized with a microemulsion method. The neutron diffraction studies and the temperature-dependent decay of magnetization show the superparamagnetic relaxation occurring in these nanoparticles. The neutron diffraction shows a high degree of inversion with the 78% tetrahedral sites occupied by Fe{sup 3+} cations. The nanoparticles with a 12 nm diameter have a blocking temperature around 320 K. The field-cooled and zero-field-cooled magnetization measurements display a divergence below the blocking temperature. The energy barrier distribution of magneticanisotropy is derived from the temperature-dependent decay of magnetization. The magneticanisotropy is clearly the origin of the divergence in the field-cooled and zero-field-cooled magnetization measurements. The energy barrier distribution function is used in a computer simulation of the zero-field-cooled magnetization, and the calculated magnetization has a great consistency with experimentally measured values. These studies on the magneticanisotropy distribution elucidate the mechanism of superparamagnetic relaxation and facilitate the design and control of superparamagnetic properties in nanoparticles.

We compared magnetic properties of epitaxial Co(111) films grown on microstep- and macrostep-bunched vicinal Si(111) substrates. A surface of the microstep-bunched Si(111) substrate represents regular array of step-bunches with height of 1.7 nm divided from each other by flat microterraces with a width of 34 nm. A surface of the macrostep-bunched Si(111) substrate is constituted by macrostep bunches with a height of 7585 nm divided by atomically flat macroterraces. The average sum width of a macrostep bunch and a macroterrace is 2.3 ?m. While in-plane magneticanisotropy was spatially uniform in Co(111) films grown on the microstep-bunched Si(111), periodic macromodulation of the topography of the Si(111) substrate induced spatial modulation of in-plane magneticanisotropy in Co(111) film grown on the macrostep-bunched Si(111) surface. The energy of uniaxial magneticanisotropy in the areas of the Co(111) film deposited on the Si(111) macrosteps was higher more than by the order of magnitude than the energy of the magneticanisotropy in the areas grown on macroterraces. Magnetization reversal in the areas with different energy of the magneticanisotropy occurred in different magneticfields. We showed the possibility of obtaining high density of domain walls in Co(111) film grown on the macrostep-bunched Si(111) by tuning the spatial step density of the Si(111) substrate.

Magnetite is a common accessory mineral in crustal rocks and exerts a dominant influence on the magneticanisotropy of rocks when present. Therefore the deformation behavior of magnetite strongly determines how magnetic fabric develops with increasing strain in a deforming rock. Here we show results from experimental deformation of magnetite-silicate aggregates in high-temperature transpressional shear experiments (1000-1200°C) under moderate shear stresses (10-130 MPa) using a gas-medium deformation apparatus. Anisotropy of magnetic susceptibility, shape preferred orientation (SPO) of magnetite, and electron backscatter diffraction (EBSD) were each used to characterize the magnetite deformation fabrics and intragrain microstructures. Magneticanisotropy and SPO each increase strongly with increasing strain, which ranged between 100-300%. An interesting feature of the deformation fabrics is that both magnetite SPO and magnetic fabric intensity are stronger at higher temperatures, indicating that strain partitioning between magnetite and the plagioclase matrix decreases at higher temperatures. Although flow laws for magnetite predict it to be weaker than dry plagioclase at the experimental conditions, the temperature-dependence of the fabric strength indicates that magnetite is more viscous than the "wet" plagioclase used in the experiments. In contrast to the magnetic and shape fabrics, crystallographic preferred orientation (CPO) of magnetite is very weak in all deformed samples. In EBSD orientation mapping of individual particles, incipient subgrain boundary formation is evident in magnetite grains, indicating that dislocation creep processes were active in magnetite despite the lack of a well-developed CPO. The weak magnetite CPOs are primarily attributed to multiple slip systems acting in parallel. These findings support the observations of previous studies that crystallographic textures in cubic minerals such as magnetite may be inherently weak or slow to develop and that CPO alone is not always a reliable indicator of deformation mechanisms.

Magneticanisotropy of LuFe11TiHx(x=0,1) single crystals and magnetically oriented powder samples of LuFe11TiNx (x=1) were investigated. The anisotropy study has been performed by means of torque and magnetization measurements. The temperature dependencies of the magnetocrystalline anisotropy constants were determined using both least-squared fitting for the corrected experimental torque curves and from the magnetization isotherms along the hard [100] direction using

The recently discovered giant magneticanisotropy of single magnetic Co atoms raises the hope of magnetic storage in small clusters. We present a joint experimental and theoretical study of the magneticanisotropy and the spin dynamics of Fe and Co atoms, dimers, and trimers on Pt(111). Giant anisotropies of individual atoms and clusters as well as lifetimes of the excited states were determined with inelastic scanning tunneling spectroscopy. The short lifetimes due to hybridization-induced electron-electron scattering oppose the magnetic stability provided by the magneticanisotropies. PMID:19659116

Three-dimensional finite strain and magnetic susceptibility anisotropy have been determined for 15 ordinary chondrites. The axes of strain and magnetic ellipsoids roughly correlate in both magnitude and orientation. The shapes of these ellipsoids are generally oblate spheroids that define a dominant foliation and a weak lineation. These characteristics suggest deformation involving uniaxial compaction. The degree of uniaxial deformation correlates with intensity of shock, as indicated by optical, TEM and chemical criteria. These data, plus the lack of a relationship between foliation and metamorphic history, indicate that dynamic processes, i.e., impacts, produced planar deformation fabrics in chondrites.

We report a more than ten-fold enhancement of magneticanisotropy in nanostructured La0.67Sr0.33MnO3 (LSMO) thin films grown epitaxially on (001) SrTiO3 substrates. We have etched periodic linear trenches in 6 nm LSMO films, and investigated magneticanisotropy in these nanostructured thin films via the planar Hall effect (PHE). These trenches have depth of 2 nm and periodicities of 200 - 400 nm. The PHE resistance of the un-patterned LSMO films exhibits sinusoidal angular dependence in an in-plane magneticfield, and shows four-fold sharp resistance switching below a critical magneticfield of 400 Oe, corresponding to a biaxial magneticanisotropy of ~ 1x105 erg/cm3 along <110>directions. In the nanostructured samples, we observe an additional two-fold resistance switching feature, which persists in magneticfields higher than 4000 Oe, corresponding to a uniaxial magneticanisotropy >1x106 erg/cm3 along one of the biaxial magnetic easy axes. This significant enhancement of magneticanisotropy cannot be accounted for by shape anisotropy or a uniform strain modulation. We also discuss the effects of the orientation and periodicity of the nano-trenches on the anisotropy enhancement.

The liquid phase epitaxy growth and characterization of single crystal (210)-oriented thin garnet films with Bi substitution up to 1.5at./f.u. is reported. These epitaxial films exhibit an easy plane of magnetization which is inclined with respect to the film plane, making them uniquely suitable for garnet-based magneto-optic imagers (MOIs). In order to identify the optimal growth conditions to attain the highest sensitivity of such MOIs, the chemical composition of the films is discussed in relation with their magnetic and optic properties. It has been demonstrated that the increase in the amount of Pr tends to increase the in-plane orthorhombic anisotropyfield HKi, while the rare-earth substitution by Bi has a strong effect on the canted orthorhombic anisotropy Kyz. The best MOI film had a saturation field of 130Oe and a sensitivity of 175deg /A.

The relationship between structure and magneticanisotropy in mono- and oligonuclear paramagnetic complexes, based on low-spin [Fe(CN)6]3 - and hexacoordinate NiII complexes with bridging CN - groups, are analyzed with special emphasis on the contributions of spin-orbit coupling and Jahn-Teller distortions as well as strain-induced distortions at the [Fe(CN)6]3 - subunit. The basic theoretical principles are described, which allow to treat the lowest multiplets of FeIII and NiII, due to the t2g ?5 and t2g ?6eg 2 electronic configurations, respectively, and their anisotropic exchange coupling. Examples are then presented, to show how small angular distortions of [Fe(CN)6]3 - lead to dramatic changes of the magneticanisotropy of the corresponding oligonuclear complexes. The nature of the lowest spin multiplet and the spin-anisotropy gap are analyzed with a combination of density functional theory and ligand field theory (LFDFT). A general ab-initio approach is also proposed, which allows to calculate the magneticanisotropy of oligonuclear complexes with transition metals in orbitally degenerate or nearly-degenerate electronic ground states.

X-ray resonant magnetic scattering was employed to study a fully reversible spin-flop transition in orthorhombic Gd{sub 5}Ge{sub 4} and to elucidate details of the magnetic structure in the spin-flop phase. The orientation of the moments at the three Gd sites flop 90{sup o} from the c axis to the a axis when a magneticfield, H{sub sf} = 9 kOe, is applied along the c axis at T = 9 K. The magnetic space group changes from Pnm'a to Pn'm'a' for all three Gd sublattices. The magneticanisotropy energy determined from experimental measurements is in good agreement with the calculations of the magneticanisotropy based on the spin-orbit coupling of the conduction electrons and an estimation of the dipolar interactions anisotropy. No significant magnetostriction effects were observed at the spin-flop transition.

(Co/Pd){sub N} multilayers exhibit high vertical magneticanisotropy and have been extensively explored as recording medium candidates for high density magnetic recording applications. In this work (Co/Pd){sub N} multilayers are deposited by magnetron sputtering and patterned into large periodic arrays of 200 nm islands to enable controlled domain wall injection for quantitative comparison of magneticanisotropy energies. Magnetic properties are correlated with x-ray photoelectron spectroscopy data, an approach commonly used to probe the binding energies and valence band positions. Confirming theoretical predictions, it is demonstrated that the degree of d-shell hybridization at Co/Pd interfaces directly correlated with the magnitude of magneticanisotropy.

Partly automated facility measures and computes steady near magneticfield produced by object. Designed to determine magneticfields of equipment to be installed on spacecraft including sensitive magnetometers, with view toward application of compensating fields to reduce interfernece with spacecraft-magnetometer readings. Because of its convenient operating features and sensitivity of its measurements, facility serves as prototype for similar facilities devoted to magnetic characterization of medical equipment, magnets for high-energy particle accelerators, and magnetic materials.

Spin-orbit torques, including the Rashba and spin Hall effects, have been widely observed and investigated in various systems. Since interesting spin-orbit torque (SOT) arises at the interface between heavy nonmagnetic metals and ferromagnetic metals, most studies have focused on the ultra-thin ferromagnetic layer with interface perpendicular magneticanisotropy. Here, we measured the effective longitudinal and transverse fields of bulk perpendicular magneticanisotropy Pd/FePd (1.54 to 2.43?nm)/MgO systems using harmonic methods with careful correction procedures. We found that in our range of thicknesses, the effective longitudinal and transverse fields are five to ten times larger than those reported in interface perpendicular magneticanisotropy systems. The observed magnitude and thickness dependence of the effective fields suggest that the SOT do not have a purely interfacial origin in our samples. PMID:25293693

The temperature dependence of the magneticanisotropy of magnetoelastic chromium-substituted cobalt ferrites (CoCrxFe 2-xO4 with 0 les x les 0.8) was investigated over the temperature range 10-400 K. The first-order cubic anisotropy coefficient K1 was calculated by fitting the high-field regimes of the major hysteresis loops to the law of approach to saturation, which is based on the assumption that

The temperature dependences of the magnetization in manganites of different composition and structural morphology were measured in two cooling regimes, field cooling (FC) and zero-field cooling (ZFC), for two different orientations of a magneticfield, parallel and perpendicular to the c-axis. The following general tendencies were found: (1) The difference between the magnetizations MFC and MZFC at T = 5 K increases with increasing magneticfield, reaching the maximum value in a magneticfield of about 2 kOe, and then drops in the range 2-5 kOe; (2) The field dependence of the "splitting" temperature T* below which the difference between the magnetizations MFC and MZFC appears can be reasonably well described by a power law with the exponent 2/3 as predicted by the theory of spin glasses. Both results are characteristic for single crystals, as well as for ceramics and films. On the other hand, the field dependence of the anisotropy of magnetic susceptibility is different for samples with different degrees of magnetic ordering (?/TC). These results are consistent with the detected in the present study universality of the line separating the low-temperature region of irreversibility in the H-T phase diagram of manganites. Deviations from the T*-H-line with the exponent 2/3 in strong magneticfields, which are commonly associated with the appearance of the magnetization component transverse to the magneticfield, are typical for samples containing the antiferromagnetic phase. The interpretation takes into account the multi-phase nature of the systems, i.e., coexistence of spin glass with ferromagnetism and antiferromagnetism. The observed change in the anisotropy of magnetic susceptibility with increasing magneticfield and the behavior of magnetic and thermomagnetic irreversibility are regarded as a manifestation of the spin-reorientation phase transition in an antiferromagnetic environment. This in turn initiates the transformation of the spin-glassfrom the Ising- to the Heisenberg-typewhich leads to the change in the exponent in the T*-H diagram from 2/3 to 2. The observed phenomenon is universalit was observed in manganites of different composition and structural morphologyand represents a particular type of polyamorphism, namely, spin-glass polyamorphism.

Density functional theory (DFT) calculations of the energy of magneticanisotropy for diluted ferromagnetic semiconductor Ge1-xMnxTe were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magneticanisotropy energy is presented. Analysis of microscopic mechanism of magneticanisotropy is provided, in particular the role of spin-orbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magneticanisotropy in rhombohedral Ge1-xMnxTe (1?1?1) thin layers. PMID:25988352

Density functional theory (DFT) calculations of the energy of magneticanisotropy for diluted ferromagnetic semiconductor Ge1?xMnxTe were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magneticanisotropy energy is presented. Analysis of microscopic mechanism of magneticanisotropy is provided, in particular the role of spinorbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magneticanisotropy in rhombohedral Ge1?xMnxTe (1?1?1) thin layers.

This is an activity about the declining strength of Earth's magneticfield. Learners will review a graph of magneticfield intensity and calculate the amount by which the field has changed its intensity in the last century, the rate of change of its intensity, and when the field should decrease to zero strength at the current rate of change. Learners will also use evidence from relevant sources to create a conjecture on the effects on Earth of a vanished magneticfield. Access to information sources about Earth's magneticfield strength is needed for this activity. This is Activity 7 in the Exploring Magnetism on Earth teachers guide.

We report a novel quantification method of tri-axial magneticanisotropy in orthorhombic substances containing rare earth (RE) ions using tri-axial magnetic alignment and tri-axial magneticanisotropies depending on the type of RE in RE-based cuprate superconductors. From the changes in the axes for magnetization in magnetically aligned powders of (RE?{sub 1?x}RE?{sub x}){sub 2}Ba{sub 4}Cu{sub 7}O{sub y} [(RE?,RE?)247] containing RE ions with different single-ion magneticanisotropies, the ratios of three-dimensional magneticanisotropies between RE?247 and RE?247 could be determined. The results in (Y,Er)247, (Dy,Er)247, (Ho,Er)247, and (Y,Eu)247 systems suggest that magneticanisotropies largely depended on the type of RE? (or RE?), even in the heavy RE ions with higher magneticanisotropies. An appropriate choice of RE ions in RE-based cuprate superconductors enables the reduction of the required magneticfield for the production of their bulks and thick films based on the tri-axial magnetic alignment technique using modulated rotation magneticfields.

Large-area, over several square centimeters, mesoporous array of magnetic nanostructure with perpendicular anisotropy is prepared by depositing Co/Pt multilayers (MLs) on a mesopore array of anodized alumina (AAO) fabricated on Si wafers. The MLs are mainly deposited on the top of AAO walls and perimeters of the pores; very small amounts of magnetic material reach the bottom due to the high aspect ratio of AAO. Consequently, ordered pores are present in the magnetic MLs. The mean pore diameter of the fabricated mesoporous array is 8.83 nm with a standard deviation of 3.16 nm and density of about 2.1 × 1011 cm-2. The Co/Pt MLs deposited on AAO and Si both exhibit strong perpendicular magneticanisotropy, but the perpendicular coercivity (Hc) increases by 15 times on AAO compared to that on Si. On the other hand, the magnetic cluster size decreases from 1000 nm (on Si) to 100 nm due to the presence of high-density pores. The dramatic increase in Hc and the decrease in magnetic cluster size suggest that the pores behave as effective pinning sites. The magnetization-switching characteristics of the fabricated porous structure are different from those of the continuous films or Stoner Wohlfarth-type (S W) particles. One of the potential applications of this mesoporous structure may be in the field of high-density magnetic data storage.

MagneticFields Analogous to electric field, a magnet produces a magneticfield, B Set up a B field two ways: Moving electrically charged particles Current in a wire Intrinsic magneticfield Basic characteristic of elementary particles such as an electron #12;MagneticFieldsMagneticfield lines Direction

Magnetotactic bacteria (MTB) synthesize intracellular single-domain (SD) magnetites or occasionally greigites magnetosomes, which are commonly assembled into chain(s) and server as navigation device in bacterial magnetotaxis. MTB are ubiquitous in aquatic environments ranging from freshwater to saline water. When MTB die, magnetosomes could be preserved in lake and marine sediments in forms of fossilized magnetosomes (also called magnetofossils). SD magnetofossils are stable carriers of natural remanent magnetization, and potential indicators for paleoenvironments. Our recent studies have revealed that MTB communities and their magnetosome formation are sensitive to oxygen, salinity, iron source and other environmental factors. Therefore, identification of magnetofossils is of great interests in the study of paleomagnetism, environmental magnetism, sedimentary magnetism and paleoenvironmental or paleoclimate reconstruction. Magnetic methods are widely used as fast, economic and effective approaches in detection of magnetofossils. Thee most distinctive features of magnetofossils are their uniformed nano-size range and unique chain structure. Consequently, anhysteretic remanent magnetization, first-order reversal curve diagram (FORC), low-temperature magnetic measurements (e.g. delta ratio, so-called the Moskowitz test) and ferromagnetic resonance (FMR) are often used for magnetic detection of magnetofossils. However, ambiguities remain because these magnetic properties can be seriously affected by magnetostatic interaction and magneticanisotropy, e.g., as the chain collapse during deposition and post-depositional diagenesis. In this paper we analyzed magnetic properties of three sets of synthesized samples containing extracted magnetosomes of the cultured Magnetospirillum magneticum strain AMB-1, to determine how the chain integrity dependent magnetostatic interaction and anisotropy influence the magnetic parameters, which in turn can be used as indication of the state of magnetofossils. Results show that intact MTB and well-dispersed magnetosome chains are characterized by strong magneticanisotropy and weak magnetostatic interactions, but progressive chain breakup and particle clumping significantly increases the degree of the magnetostatic interaction and a change of magnetic signature towards the typical properties of interacting, single-domain particles. Specifically, the progressive chain breakup and particle clumping systematically decrease of the ratio of anhysteretic remanent magnetization to the saturation isothermal remanent magnetization (ARM/SIRM or ?ARM/SIRM), the crossing point of the Wohlfarth-Cisowski test, and the delta ratio (?FC/?ZFC) between losses of field and zero-field cooled remanent magnetization across the Verwey transition. We hence propose a delta-plot (?FC/?ZFC vs. ?ZFC) as a new approach to diagnose magnetosome chains of magnetosomes, and detect magnetofossils in sediments and rocks.

Analytic calculations of the cosmological density fluctuations and microwave background radiation anisotropies induced by gradients in a topologically trivial scalar field are presented. This anlaytic solution should provide a good test for numerical simulations of microwave anisotropy from scalar fields. To the extent that these results generalize to other scalar field models and configurations, they imply that (1) MBR measurements limit large-scale primordial variations greater than about 5[times]10[sup 16] GeV within our horizon, (2) the total scalar field variation is a fair predictor of the magnitude of the MBR anisotropy, but is only accurate to within a factor of about three, (3) scalar fields as well as other models of seeded perturbations produce a few times more anisotropy [Delta][ital T]/[ital T] for a given density fluctuation [delta][rho]/[rho] (on the same scale) than do primordial adiabatic perturbations, (4) models of scalar field seeds which produce a scale-invariant spectrum of perturbations seem to require galaxies to be more clustered than the mass on small scales, and (5) scalar fields do not tilt'' the Universe.

A generalized mean magneticfield induction equation for differential rotators is derived, including a compressibility, and the anisotropy induced on the turbulent quantities from the mean magneticfield itself and a mean velocity shear. Derivations of the mean field equations often do not emphasize that there must be anisotropy and inhomogeneity in the turbulence for mean field growth. The anisotropy from shear is the source of a term involving the product of the mean velocity gradient and the cross-helicity correlation of the isotropic parts of the fluctuating velocity and magneticfield, $\\lb{\\bfv}\\cdot{\\bfb}\\rb^{(0)}$. The full mean field equations are derived to linear order in mean fields, but it is also shown that the cross-helicity term survives to all orders in the velocity shear. This cross-helicity term can obviate the need for a pre-existing seed mean magneticfield for mean field growth: though a fluctuating seed field is necessary for a non-vanishing cross-helicity, the term can produce linear (in time) mean field growth of the toroidal field from zero mean field. After one vertical diffusion time, the cross-helicity term becomes sub-dominant and dynamo exponential amplification/sustenance of the mean field can subsequently ensue. The cross-helicity term should produce odd symmetry in the mean magneticfield, in contrast to the usually favored even modes of the dynamo amplification in sheared discs. This may be important for the observed mean field geometries of spiral galaxies. The strength of the mean seed field provided by the cross- helicity depends linearly on the magnitude of the cross-helicity.

This demonstration of the magneticfield lines of Earth uses a bar magnet, iron filings, and a compass. The site explains how to measure the magneticfield of the Earth by measuring the direction a compass points from various points on the surface. There is also an explanation of why the north magnetic pole on Earth is actually, by definition, the south pole of a magnet.

The grand challenge for this legacy cycle unit is for students to design a way to help a recycler separate aluminum from steel scrap metal. In previous lessons, they have looked at how magnetism might be utilized. In this lesson, students think about how they might use magnets and how they might confront the problem of turning the magneticfield off. Through the accompanying activity students explore the nature of an electrically induced magneticfield and its applicability to the needed magnet.

Students use a compass and a permanent magnet to trace the magneticfield lines produced by the magnet. By positioning the compass in enough spots around the magnet, the overall magnetfield will be evident from the collection of arrows representing the direction of the compass needle. In activities 3 and 4 of this unit, students will use this information to design a way to solve the grand challenge of separating metal for a recycling company.

Students use the same method as in the activity from lesson 2 of this unit to explore the magnetism due to electric current instead of a permanent magnet. Students use a compass and circuit to trace the magneticfield lines induced by the electric current moving through the wire. Students develop an understanding of the effect of the electrical current on the compass needle through the induced magneticfield and understand the complexity of a three dimensional field system.

The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magneticfield experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magneticfield of Neptune and an associated magnetosphere and magnetic tail. A maximum magneticfield of nearly 10,000 nanoteslas (1 nanotesla = 10â»âµ gauss) was observed near closest approach, at a

We used first-principles methods to calculate the electronic and magnetic structure of Co/Ni(111) superlattices with a thickness of the Co and Ni layers ranging from one to four monolayers. We give a detailed database on the magnetocrystalline anisotropy energy induced by interfaces and on the total magneticanisotropy energy including the shape anisotropy of the superlattices. The magneticanisotropy is analyzed in terms of the anisotropy of the Co and Ni orbital magnetic moments and in terms of the electron states of the superlattices. Most of our results apply to superlattices with an fcc stacking of the atomic layers, but we also study the influence of stacking faults on the anisotropy. We describe the magnetization, and the density of states and spin polarization at the Fermi level of all these superlattices. The database which we provide should help researchers who aim to design Co/Ni-based magnetic or spintronic devices with suitable physical properties.

We study the equilibrium phase diagram of ultrathin chiral magnets with easy-plane anisotropy A . The vast triangular skyrmion lattice phase that is stabilized by an external magneticfield evolves continuously as a function of increasing A into a regime in which nearest-neighbor skyrmions start overlapping with each other. This overlap leads to a continuous reduction of the skyrmion number from its quantized value Q =1 and to the emergence of antivortices at the center of the triangles formed by nearest-neighbor skyrmions. The antivortices also carry a small "skyrmion number" QA?1 that grows as a function of increasing A . The system undergoes a first order phase transition into a square vortex-antivortex lattice at a critical value of A . Finally, a canted ferromagnetic state becomes stable through another first order transition for a large enough anisotropy A . Interestingly enough, this first order transition is accompanied by metastable meron solutions.

Magnetic properties of iron films grown on Au layers with different thicknesses on a W(110) surface are studied with spin polarized low energy electron microscopy. The iron thickness for the onset of ferromagnetic order depends approximately linearly on the thickness of underlying gold film. The easy axis direction also depends upon the Au thickness. It is parallel to the tungsten [Formula: see text] direction at the onset of magnetization for one and two monolayers of gold. For thicker gold films the easy axis is parallel to the [001] direction. The direction of the easy axis and the onset of ferromagnetic order are discussed in terms of magneticanisotropies, interaction between the iron overlayer, gold and tungsten substrate, Fe film strain and morphology. PMID:21828573

The thermal stability of pinned synthetic ferrimagnets with perpendicular anisotropy is investigated. These structures consist of two [Pt\\/Co] mutilayers (MLs) antiferromagnetically coupled through a Ru spacer, in which one of them is, in turn, exchange biased with FeMn. The switching fields of both MLs can be tuned, at a given temperature, by varying the relative number of (Pt\\/Co) repeats comprised

An analysis of the magnetoelastic coupling and the magnetocrystalline anisotropy in rare earth intermetallic compounds has been undertaken on the basis of a microscopic description. Crystal electric field and exchange interaction have been considered as the main contribution to the free energy in order to explain the behaviour. Magnetostriction measurements on cubic (RAl2, RNi2) and uniaxial (RCo5 and R2Fe14B) compounds

Due to the unique attribute of perpendicular magneticanisotropy (PMA), [Co/Pt]n multilayers have both scientific and technological importance. [Co/Pt]n multilayers and their associated properties are presented, including (1) magnetization reversal in [Co/Pt]n multilayers with different repeat number n; and (2) antisymmetric magnetoresistance in [Co/Pt]n multilayers. Magnetization reversal in [Co/Pt]n multilayers with PMA has been found to depend sensitively on the repeat number n. In [CO/Pt]n multilayers with a large n (e.g. n=16) or a small n (e.g. n=2), magnetization reversal is dominated by nucleation or domain wall motion, respectively. Magnetization reversal in [Co/Pt]n multilayers with an intermediate n=4 provides a glimpse of the intermediate regime. During the first order reversal process, the magnetization of the [Co/Pt]4 multilayer first decreases, then reaches a plateau, and finally rises back to saturation, corresponding to expanding bubble domains, stationary domains, and domains with unchanged boundaries but fading contrast, respectively. MFM imaging reveals the existence of many submicron-sized unreversed channels within the boundary of the bubble domains, which cause the fading contrast. These unusual reversal behaviors in the [CO/Pt]4 multilayer are due to thermally activated domain wall motion, confirmed by the studies of the time dependence of magnetization. Numerical simulations show that the dependence of magnetization reversal on n is mainly due to the demagnetizing effect. Intrinsic magnetoresistance (MR), regardless of mechanisms, is symmetric with respect to the magneticfield H. A new form of MR, which is antisymmetric in H, has been demonstrated in [Co/Pt]n multilayers with PMA. By performing simultaneous MOKE imaging and transport measurements on a Pt/Co wedge/Pt trilayer with a controlled two-domain structure, it has been conclusively shown that the antisymmetric MR originates from the Hall fields due to extraordinary Hall effect on either side of the domain wall. The observed MR and Hall results can be quantitatively accounted for by a circulating-current model. This rare occurrence of antisymmetric MR is due to the special geometry afforded in multilayers with PMA, where the magnetization, current, and domain wall directions are mutually perpendicular.

The anisotropy of magnetic susceptibility of some basic igneous and metamor- phic rocks has been found to be due to the preferred orientation of the long axes of grains of magnetite. The degree of anisotropy is in a few samples as great as 40 per cent but usually is less than 10 per cent. The variation in anisotropy is believed

width and superimposed on the weak six-fold magnetocrystalline anisotropy. Furthermore, on the basis was continuously tuned. The six-fold magnetocrystalline anisotropy superimposed on a weak UMA can be characterizedTuning magneticanisotropies of Fe films on Si(111) substrate via direction variation of heating

A twisted magnetic structure in Ni ultrathin films attached to antiferromagnetic FeMn is revealed by a combination of the depth-resolved x-ray magnetic circular dichroism (XMCD) and the polarized neutron reflectivity (PNR) techniques. The depth-resolved XMCD at remanent magnetization shows that the perpendicular magnetization component in the Ni film decreases around the interface to FeMn when the film exhibits perpendicular magnetization, whereas the in-plane component is kept constant through the whole film in the case of in-plane magnetization. Moreover, the PNR data shows that when a weak in-plane magneticfield is applied to a film, which exhibits perpendicular magnetization at the remanent state, an in-plane magnetization component is induced in Ni around the interface to FeMn. These results are reasonably interpreted by assuming that the magnetic moment in the Ni layer is twisted from the perpendicular to the in-plane directions towards the interface to FeMn. Such a magnetic structure is supposed to be induced by a magneticanisotropy interaction at the interface between ferromagnetic Ni and antiferromagnetic FeMn, which makes the Ni magnetic moment around the interface rotate towards the in-plane direction.

We have studied the variation of perpendicular magneticanisotropy (PMA) of CoFeB layers with the oxidation degree of the MgO buffer layers. After annealing at 330 °C, the out-of-plane anisotropyfield (Hk) of 1.5-nm CoFeB could be optimized to 3.1 kOe. To investigate the orbital hybridization of the Fe-3d and O-2p, the orbital moments per hole (morb/Nh) of Fe in annealed CoFeB layers were extracted by using x-ray magnetic circular dichroism. The dependence of morb/Nh on the oxidation time of MgO coincided with that of Hk, which revealed that PMA of annealed CoFeB originated from the interfacial orbital hybridization.

We present full ab initio calculations of giant magnetoresistance (GMR) in Co/Cu (001) multilayers including self-consistent impurity scattering potentials. Starting from density functional theory the electronic structure of the multilayer and the scattering at impurities are described by means of a new Green function method. It will be demonstrated that impurity scattering in magnetic multilayers is strongly anisotropic in comparison to impurity scattering in bulk systems. Concerning transport the anisotropy of scattering leads to a formation of highly conducting channels which give rise to short circuits and cause strong variation of GMR as a function of the impurity position in the multilayer. {copyright} 2001 American Institute of Physics.

Knowledge on the nature of magneticfields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magneticfields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

The above animations represent two typical bar magnets each with a North and South pole. The arrows represent the direction of the magneticfield. The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black. You may drag either magnet and double-click anywhere inside the animation to add a magneticfield line, and mouse-down to read the magnitude of the magneticfield at that point.

We report the characterization of the magnetic properties of polycrystalline disks of Ni72Mn28 and Ni(72-x)Mn28Ptx (x=1.0, 4.0, and 10.0) at 4.2 K induced by field cooling (FC). It is found that the FC-induced anisotropyfield HK, and coercivity HC, are strongly enhanced by the addition of Pt impurities. The remanent magnetization in the direction of the initial applied field (in the disk plane) for each samples can be rotated from 0° to 180° and back to 0° in various stationary fields above and below HK and the parallel component is measured (the longitudinal magnetization component ML). From the analysis of the angular dependence of ML, we show that these results can be accounted for by the coexistence of Mn(Ni)-rich and/or Mn(Ni)-deficient nanoscale regions coupled antiferromagnetically. It is found that the unidirectional anisotropy originates from interfacial exchange interactions between these regions. Up to some critical angle rotation (?c) relative to H, the unidirectional anisotropyfield turns rigidly with the sample, while above ?c, the coupled regions become unstable and magnetically rearrange such that a unidirectional anisotropy is induced along H. The value of ?c varies from region to region. An increase in HK and HC with increasing Pt content can be attributed to the increase in the number of antiferromagnetically coupled regions of decreasing size. In addition, it is found that some ordered single-domain clusters (presumably Ni3Mn compound) are distributed within the disordered Ni or Mn-rich regions.

Oriented magnetic nanoparticles have been suggested as a good candidate for a magnetic sensor in ants. Behavioural evidence for a magnetic compass in neotropical leaf-cutter ants, Atta colombica (Formicidae: Attini), motivated a study of the arrangement of magnetic particles in the ants four major body parts by measuring the angular dependence of the ferromagnetic resonance spectra at room temperature. Spectra of the thoraces and those of the abdomens showed no significant angular dependence, while those of the antennae and those of the heads exhibited a periodic dependence relative to the magneticfield. Fitting of the angular dependence of the resonant field resulted in an unexpected magneticanisotropy with uniaxial symmetry. High values of the first order anisotropy constant were observed for the magnetic material in antennae (?2.9? × ?105?erg?cm?3) and heads (?1? × ?106?erg?cm?3) as compared to body parts of other social insects. In addition, the magnitude of the anisotropy in the heads was comparable to that observed in magnetite nanoparticles of 45?nm diameter. For the antennae, the mean angle of the particles easy magnetization axis (EA) was estimated to be 41° relative to the straightened antennas long axis. For the heads, EA was approximately 60° relative to the heads axis running from midway between the spines to the clypeus. These physical characteristics indicate organized magnetic nanoparticles with a potential for directional sensitivity, which is an important feature of magnetic compasses.

The magnetization behavior, magneticanisotropy, and domain configurations of Co/Pd multilayers with perpendicular magneticanisotropy capped with permalloy is investigated using magnetometry, magnetic force microscopy, and ferromagnetic resonance. The thickness of the Ni80Fe20 layer in [Co/Pd ] 5/NiFe (t ) was varied from t =0 to 80 nm in order to study the interplay between the anisotropy and magnetization directions of Co/Pd and NiFe. By varying the thickness of the NiFe layer, the net anisotropy changes sign, but domains with plane-normal magnetization are present even for the thickest NiFe. Ferromagnetic resonance measurements show a decrease in damping with increasing NiFe thickness. The results demonstrate how the magnetic behavior of mixed-anisotropy thin films can be controlled.

Using first-principles calculations, we investigated the impact of chromium (Cr) and vanadium (V) impurities on the magneticanisotropy and spin polarization in Fe/MgO magnetic tunnel junctions. It is demonstrated, using layer resolved anisotropy calculation technique, that while the impurity near the interface has a drastic effect in decreasing the perpendicular magneticanisotropy (PMA), its position within the bulk allows maintaining high interfacial PMA while reducing the bulk magnetization and correlatively the easy-plane demagnetizing energy. As a result, the effective magneticanisotropy tends to increase as a function of the Cr or V concentration resulting in an increase in the critical magnetic thickness at which the crossover from out-of-plane to in-plane anisotropy takes place. At the same time, the interfacial spin polarization is not affected by the magnetic layer bulk doping by Cr or V impurities and even enhanced in most situations thus favoring an increase of tunnel magnetoresistance (TMR) amplitude.

We study the effects of the temperature and of a magneticfield in the setup of an intersection of D3/D7 branes, where a large number of D7 branes is smeared in the transverse directions to allow for a perturbative solution in a backreaction parameter. The magneticfield sources an anisotropy in the plasma, and we investigate its physical consequences for the thermodynamics and energy loss of particles probing the system. In particular we comment on the stress-energy tensor of the plasma, the propagation of sound in the directions parallel and orthogonal to the magneticfield, the drag force of a quark moving through the medium and jet quenching.

CoO/Fe/Ag(001) films were grown epitaxially and studied by X-ray Magnetic Circular Dichroism (XMCD) and X-ray Magnetic Linear Dichroism (XMLD). After field cooling along the Fe[100] axis to 80 K, exchange bias, uniaxial anisotropy, and 4-fold anisotropy of the films were determined by hysteresis loop and XMCD measurements by rotating the Fe magnetization within the film plane. The CoO frozen spins were determined by XMLD measurement as a function of CoO thickness.We find that among the exchange bias, uniaxial anisotropy, and 4-fold anisotropy, only the uniaxial magneticanisotropy follows thickness dependence of the CoO frozen spins.

The perpendicular magneticanisotropy (PMA) and dynamic magnetization-reversal process in [CoFeB t nm/Pd 1.0 nm]n(t = 0.4, 0.6, 0.8, 1.0 and 1.2 nm n = 2 ? 20) multilayer films have been studied by means of magnetic hysteresis and Kerr effect measurements. Strong and controllable PMA with an effective uniaxial anisotropy up to 7.7 × 106 Jm?3 and a saturation magnetization as low as 200 emu cm?3 are achieved. The surface/interfacial anisotropy of the CoFeB/Pd interfacesthe main contribution to the PMAis separated from the effective uniaxial anisotropy of the films and appears to increase with the number of CoFeB/Pd bilayers. Observation of the magnetic domains during a magnetization-reversal process, using polar magneto-optical Kerr microscopy, reveals the detailed behavior of the nucleation and displacement of the domain walls.

Turbulence heats the solar wind as it expands away from the Sun, but where and how does heating of ions and electrons occur? In order to understand this we must first look at the fluctuations making up the cascade, the properties and anisotropies of which will determine whether ions or electrons are heated and whether field-parallel or -perpendicular heating will occur, all of which amounts to a lot of different anisotropies! With this in mind, we present a review of recent advances in the observation of plasma turbulence in the solar wind and comparison with simulations; which features of solar wind turbulence are well reproduced and which need to be captured better? The first anisotropy is that of the fluctuations making up the turbulent cascade itself, fluctuations are known to be highly transverse, meaning that the perpendicular magneticfield components are dominant over the field-parallel component. The second anisotropy is that of the scaling of amplitude towards smaller scales with steeper spectra parallel to the local magneticfield direction. Observations of the anisotropy of the full power spectral tensor will be discussed, in particular with reference to Alfvenic and pseudo-Alfvenic fluctuations (effectively two different polarizations of Alfven waves), the next step beyond the traditional "slab + 2D" approach to incompressible MHD turbulence. The third anisotropy is that of the ion and electron distributions. Both sets of charged particles frequently show non-Maxwellian distributions with higher temperatures found either perpendicular to or parallel to the magneticfield direction. Proton distributions often show beams and the heavier alpha particles are often hotter than the protons. Localized structures such as current sheets and magnetic discontinuities are shown to be sites of intense and anisotropic heating. Small scale fluctuations filling the space between such discontinuities may also dissipate energy into ions and electrons, either through electric fields intrinsic to the modes generated by the turbulence or through resonant or stochastic processes. Observations show that kinetic Alfven waves are the dominant mode.

{ital Ab} {ital initio} electronic structure calculations for the intermetallic compound UGa{sub 2} were performed using an optimized linear combination of atomic orbitals method based on the local spin density approximation. Three separate calculations were done treating the uranium 5{ital f} states as band states and as localized states with occupation two and three, respectively. In the itinerant approach, spin and orbital moments, magnetocrystalline anisotropy, and the Sommerfeld constant were calculated and found to deviate significantly from the related experimental data. In the localized approach, crystal field parameters were obtained for the 5{ital f} states, which have been treated by self-interaction corrected local-density theory. This approach with 5{ital f}{sup 2} occupation is shown to provide reasonable results for the anisotropy of the susceptibility, for the field dependence of the magnetic moments, and for the Sommerfeld constant. {copyright} {ital 1996 The American Physical Society.}

This is a lesson about the magneticfield of a bar magnet. The lesson begins with an introductory discussion with learners about magnetism to draw out any misconceptions that may be in their minds. Then, learners freely experiment with bar magnets and various materials, such as paper clips, rulers, copper or aluminum wire, and pencils, to discover that magnets attract metals containing iron, nickel, and/or cobalt but not most other materials. Next, learners experiment with using a magnetic compass to discover how it is affected by the magnet and then draw the magneticfield lines of the magnet by putting dots at the location of the compass arrow. This is the first lesson in the first session of the Exploring Magnetism teacher guide.

This webpage is part of the University Corporation for Atmospheric Research (UCAR) Windows to the Universe program. It describes the nature and configuration of magneticfields, which are the result of moving electric charges, including how they cause magnetic objects to orient themselves along the direction of the magnetic force points, which are illustrated as lines. Magneticfield lines by convention point outwards at the north magnetic pole and inward at the south magnetic pole. The site features text, scientific illustrations and an animation. Text and vocabulary are selectable for the beginning, intermediate, or advanced reader.

We performed a theoretical and experimental investigation of the quasi-static magnetic properties of anisotropic systems. We considered a modified Stoner-Wohlfarth model to describe anisotropic systems, and a distribution function to express the magneticanisotropy dispersion. We also proposed a procedure to calculate the magnetic properties from experimental results of the quadrature of magnetization curves, thus quantifying the magneticanisotropy dispersion. To test the robustness of the approach, we applied the theoretical model to describe the quasi-static magnetic properties of amorphous FeCuNbSiB ferromagnetic films, and directly compared the theoretical results with longitudinal and transverse magnetization curves measured for the films. Our films are characterized by anisotropyfields between 7 and 10.5 Oe, values compatible with that obtained for several amorphous magnetic materials, as well as by anisotropy dispersions expressed by exponents n between 14 and 30. Thus, the excellent agreement between numerical calculation and experimental results provides support to confirm the validity of our theoretical approach to describe the magnetic properties of anisotropic amorphous ferromagnetic films.

La0.7Sr0.3MnO3 (LSMO) is a promising material for spintronics applications due to its half-metallic nature. To successively exploit LSMO, both the magneticanisotropy (MA) and damping need to be well understood and, ultimately, controlled. Here, we study 30 nm epitaxial LSMO thin films grown by pulsed laser deposition on TiO2 terminated (001)SrTiO3. By means of angle- and frequency dependent ferromagnetic resonance (FMR) at room temperature, we separate various contributions to the in-plane MA: i) The four-fold magnetocrystalline anisotropy is present but negligibly small. ii) The strongest contribution Buni = 4.2 mT is uniaxial with EA along [010]. While uniaxial MA in LSMO systems is commonly related to terrace formation from the substrate miscut, we find that the terrace direction and the MA symmetry axes do not correlate, indicating a different origin of the MA. By evaluating the FMR linewidth, three nonlinear magnetic damping channels due to the two-magnon scattering are found: j) The dominant four-fold contribution with maxima along < 100 > axes emerges due to the crystalline defects. jj) A two-fold contribution with the maximum along [010] and jjj) a small two-fold contribution with maximum perpendicular to the terraces are identified.

In sintered (Nd1-xSmxDy)(FeCo)B magnets, the contributions of "soft" (Nd1-xSmxDy)2(FeCo)2B and "hard" (Nd1-xSmxDy)2(FeCo)14B phases to the temperature and field dependences of magnetization have been distinguished. The increase in Sm concentration up to 3% provides stronger interlattice RE-TM (RErare-earth metals, TMtransition metals) exchange interaction. Contributions of the NdDy and Sm to magneticanisotropy have been determined. The competition between the positive contribution of Nd and Dy and the negative contribution of Sm ions results in non-monotonous temperature and Sm concentration dependencies of anisotropyfield. Anisotropy of the studied alloys is intermediate between "easy axis" and "easy plane" symmetry.

Three complexes of the form [Ln(III)3(OQ)9] (Ln = Gd, Tb, Dy; OQ = 8-quinolinolate) have been synthesized and their magnetic properties studied. The trinuclear complexes adopt V-shaped geometries with three bridging 8-quinolinolate oxygen atoms between the central and peripheral eight-coordinate metal atoms. The magnetic properties of these three complexes differ greatly. Variable-temperature direct-current (dc) magnetic susceptibility measurements reveal that the gadolinium and terbium complexes display weak antiferromagnetic nearest-neighbor magnetic exchange interactions. This was quantified in the isotropic gadolinium case with an exchangecoupling parameter of J = -0.068(2) cm(-1). The dysprosium compound displays weak ferromagnetic exchange. Variable-frequency and -temperature alternating-current magnetic susceptibility measurements on the anisotropic cases reveal that the dysprosium complex displays single-molecule-magnet behavior, in zero dc field, with two distinct relaxation modes of differing time scales within the same molecule. Analysis of the data revealed anisotropy barriers of Ueff = 92 and 48 K for the two processes. The terbium complex, on the other hand, displays no such behavior in zero dc field, but upon application of a static dc field, slow magnetic relaxation can be observed. Ab initio and electrostatic calculations were used in an attempt to explain the origin of the experimentally observed slow relaxation of the magnetization for the dysprosium complex. PMID:24520896

We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magneticanisotropyfields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights.

Recent developments in stable radical chemistry have afforded "heavy atom" radicals, neutral open-shell (S = 1/2) molecular species containing heavy p-block elements (S, Se), which display solid-state magnetic properties once considered exclusive to conventional metal-based magnets. These highly spin-delocalized radicals do not associate in the solid state and yet display extensive networks of close intermolecular interactions. Spin density on the heavy atoms allows for increased isotropic and spin-orbit mediated anisotropic exchange effects. Structural variations induced by chemical modification and physical pressure, coupled with ab-initio methods to estimate exchange energies, have facilitated the development of predictive structure/property relationships. These results, coupled with detailed theoretical analyses and magnetic resonance spectroscopic measurements, have provided insight into the magnetic structure of ferromagnetic and spin-canted antiferromagnetic ordered materials as well as an understanding of the importance of spin-orbit coupling contributions to magnetic hysteresis and anisotropy. Isotropic and anisotropic ferromagnetic exchange can also be enhanced indirectly by the incorporation of heavy atoms into nonspin-bearing sites, where they can contribute to multi-orbital spin-orbit coupling. PMID:25767934

Controlled alignment of nanomaterials over large length scales (>1 cm) presents a challenge in the utilization of low-cost solution processing techniques in emerging nanotechnologies. Here, we report on the lyotropic liquid crystalline behavior of transition-metal-doped zinc oxide nanowires and their facile alignment over large length scales under external fields. High aspect ratio Co- and Mn-doped ZnO nanowires were prepared by solvothermal synthesis with uniform incorporation of dopant ions into the ZnO wurtzite crystal lattice. The resulting nanowires exhibited characteristic paramagnetic behavior. Suspensions of surface-functionalized doped nanowires spontaneously formed stable homogeneous nematic liquid crystalline phases in organic solvent above a critical concentration. Large-area uniaxially aligned thin films of doped nanowires were obtained from the lyotropic phase by applying mechanical shear and, in the case of Co-doped nanowires, magneticfields. Application of shear produced thin films in which the nanowire long axes were aligned parallel to the flow direction. Conversely, the nanowires were found to orient perpendicular to the direction of the applied magneticfields. This indicates that the doped ZnO possesses magnetocrystalline anisotropy sufficient in magnitude to overcome the parallel alignment which would be predicted based solely on the anisotropic demagnetizing field associated with the high aspect ratio of the nanowires. We use a combination of magnetic property measurements and basic magnetostatics to provide a lower-bound estimate for the magnetocrystalline anisotropy. PMID:21905709

There is public health concern raised by epidemiological studies indicating that extremely low frequency electric and magneticfields generated by electric power distribution systems in the environment may be hazardous. Possible carcinogenic effects of magneticfield in combination with suggested oncostatic action of melatonin lead to the hypothesis that the primary effects of electric and magneticfields exposure is a reduction of melatonin synthesis which, in turn, may promote cancer growth. In this review the data on the influence of magneticfields on melatonin synthesis, both in the animals and humans, are briefly presented and discussed. PMID:12019358

We present a model of homoionic, equal-spin s1 dimer single molecule magnets exhibiting D2h , C2v , or S2 molecular group symmetry, focusing upon the simplest D2h case. The spins within each dimer interact via the Heisenberg and the most general set of four quadratic anisotropic spin interactions with respective strengths J and {Jj} , and with the magnetic induction B . We solve the model exactly for s1=1/2 , and analytically for B along the crystal directions and numerically for other B directions for s1=1 and 5/2, and present M(B) curves at low T for these cases with antiferromagnetic Heisenberg couplings (J<0) . Low- T CV(B) curves for s1=1/2 and electron paramagnetic susceptibility ?(B,?) for s1=1 are also provided. For weakly anisotropic dimers, the Hartree approximation, or strong exchange limit, yields rather simple analytic formulas for M(B) and CV(B) at arbitrary s1 that accurately fit the exact solutions at sufficiently low T or large B . Low- T , large- B formulas for the inelastic neutron-scattering cross section S(B,q,?) and ?(B,?) with arbitrary s1 and B in the Hartree approximation are also given. For antiferromagnetic Heisenberg couplings (J<0) and weak anisotropy interactions (?Jj/J??1) , we provide analytic formulas for the 2s1 level-crossing magnetic inductions Bs,s1lc(?,?) , at which the low- T magnetization M(B) exhibits steps and the low- T specific heat CV(B) exhibits zeroes, surrounded by double peaks of uniform height. Strong anisotropy interactions drastically alter these behaviors, however. Our results are discussed with regard to existing experiments on s1=5/2Fe2 , s1=3/2Cr2 , and s1=1Ni2 dimers, suggesting the presence of single-ion anisotropy in three of them, but apparently without any sizeable anisotropic exchange interactions. Further experiments on single crystals of these and higher-spin dimers are therefore warranted, and we particularly urge further electron paramagnetic resonance and inelastic neutron-scattering experiments to be performed.

The giant magnetoresistance (GMR) of magnetic multilayers is usually considered as isotropic, i.e., independent of the direction of the sensing current with respect to the applied field. In spin-valve samples of the form NiFe/Cu/NiFe/FeMn it is possible to accurately determine the amplitude of the GMR (without any contribution from the usual anisotropic magnetoresistance) for various direction of the current with respect to the direction of the magnetization of the two ferromagnetic layers, both in the parallel and antiparallel magnetic configurations. In three series of spin-valve samples of the composition F tF/Cu tCu/NiFe/FeMn, we have observed that the GMR amplitude is larger when the current is perpendicular to the magnetizations than when it is parallel to it. This intrinsic anisotropy in the GMR shows a pronounced maximum (relative amplitude of the anisotropy of the order of 10% at the maximum) for a thickness of the ferromagnetic layer of the order of 150 Å. In contrast, this anisotropy depends very weakly on the nonmagnetic spacer layer thickness. The results are compared with semiclassical calculations of Rijks et al. [Phys. Rev. B 51, 283 (1995)]. On another respect, we have measured the in-plane (CIP) and perpendicular to the plane (CPP) giant magnetoresistance of antiferromagnetically coupled (NiFe/Ag) multilayers. Particular attention has been paid on the variation of resistivity with the angle ?? between the magnetization in the successive magnetic layers. While the CIP GMR varies almost linearly with cos(??), the CPP GMR shows strong deviations from linearity especially at large NiFe thicknesses. The results are discussed in terms of relative role of s-like and d-like electrons in CIP and CPP transport.

It has been shown that nano-sized particles of cobalt ferrite produced by the coprecipitation method for use in magnetic fluids exhibit multiaxial anisotropy, which has not previously been reported for ferrite particles. The value of the magneticanisotropy constant calculated from measurements of the decay of remanence is similar to that reported for bulk cobalt ferrite.

The influence of a gate voltage on magneticanisotropy is investigated in a thin Fe film epitaxially grown on a Ag(1,1,10) substrate and covered by MgO. Oscillations in step-induced magneticanisotropy due to quantum well ...

Electronic structure and magnetic properties of Sm2Fe17Nx are studies on the basis of the first-principles electronic structure calculation in the framework of the density functional theory within the local density and coherent potential approximations. The magneticanisotropy of the system as a function of nitrogen concentration x is discussed by taking account not only of the crystal field effects but also of the effects of the f-electron transfer from Sm to the neighboring sites. Also discussed is the magnetic transition temperature that is estimated by mapping the system into a Heisenberg model. The results show the crystalline magneticanisotropy changes its direction from in-plane to uniaxial ones as x increases. It takes the maximum value near x ~ 2 . 8 and then decreases slightly towards x = 3 . The mechanism for these behaviors is discussed in the light of the results of detailed calculations on the bonding properties between Sm and its neighboring N. This work was partly supported by Elements Strategy Initiative Center for Magnetic Materials Project, the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Arrays of circular and eliptical antidots with interhole distances much larger than hole dimensions have been fabricated by electron beam lithography and plasma etching on amorphous magnetic films with a well defined uniaxial anisotropy. In this diluted regime, each hole can be considered as an isolated inclusion in the homogeneous film. The effect of patterning is a moderate increase in

We present a model of equal spin s1 dimer single molecule magnets. The spins within each dimer interact via the Heisenberg and the most general set of four quadratic anisotropic spin interactions with respective strengths J and Jj, and with the magnetic induction B. For antiferromagnetic Heisenberg couplings (J<0) and weak anisotropy interactions (|Jj/J|1), the low temperature T magnetization M(B) exhibits 2s1 steps, the height and midpoint slope of the sth step differing from their isotropic limits by corrections of O(Jj/J)^2, but the position occurring at the energy level-crossing magnetic induction Bs,s1^lc(,), where , define the direction of B. We solve the model exactly for s1=1/2, 1, and 5/2. For weakly anisotropic dimers, the Hartree approximation yields analytic formulas for M(B) and CV(B) at arbitrary s1 that accurately fit the exact solutions at sufficiently low T or large B. Low-T formulas for the inelastic neutron scattering S(q,?) and the EPR ?(?) in an extended Hartree approximation are given. Our results are discussed with regard to existing experiments on s1=5/2 Fe2 dimers, suggesting further experiments on single crystals of these and some s1=9/2 [Mn4]2 dimers are warranted.

For some years now laminated cards containing a green, magnetically sensitive film have been available from science education suppliers. When held near a magnet, these cards appear dark green in regions where the field is perpendicular to the card and light green where the field is parallel to the card. The cards can be used to explore the magneticfield near a variety of magnets as well as near wire loops. In this paper we describe how to make these cards and how we have used them in our physics classrooms and labs.

The combination of Pt with Co either in alloy or in multilayer form is widely studied among the potential magnetic media for ultrahigh density magnetic recording. On the other hand the combination of Co with Cr in alloy form is currently providing commercial magnetic media. In an effort to further exploit and benefit from both systems, we fabricated Co(1-x)Cr(x)/Pt multilayers with two adjustable parameters. The first one is the Cr concentration on CoCr layer (x = 0, 5, 30), which modulates segregation effects on Co grains, thus tunes macroscopic magnetic features such as saturation magnetization and coercive field. The second one is the small layer thickness (< or = 0.6 nm) that affects interlayer coupling, perpendicular magneticanisotropy and magnetization enhancement through spin polarization of Pt atoms in a ferromagnetic environment. The X-ray diffraction patterns verified the existence of multilayered structures following a preferable face-centered-cubic stacking. The Pt thickness and Cr concentration are found to significantly affect the macroscopic magnetic behavior. It is remarkable the fact that, samples present perpendicular anisotropy that scales with Pt thickness and temperature, even in the case of significant Cr concentration (30% in the alloy) when ferromagnetic behavior is expected to diminish according to relevant studies in alloys and in bulk films. Such an effect may be attributed to spin-polarization of Pt interlayers and was evidenced by X-ray magnetic circular dichroism. The spin-polarization of Pt is also the drive for the strong magneto-optic enhancement in the ultra-violet region between 4.5 and 5 eV shown by magnetooptic Kerr spectroscopy. PMID:21133152

The magneticfield line Hamiltonian and the associated canonical form for the magneticfield are important concepts both for understanding toroidal plasma physics and for practical calculations. A number of important properties of the canonical or Hamiltonian representation are derived and their importance is explained.

Most of the visible matter in the Universe is in a plasma state, or more specifically is composed of ionized or partially ionized gas permeated by magneticfields. Thanks to recent advances on the theory and detection of cosmic magneticfields there has been a worldwide growing interest in the study of their role on the formation of astrophysical sources

In this lesson from Math Machines, students will learn about the effects of magneticfields on moving, electrically charged particles. The activity consists of two exercises. The first involves analyzing how a robot is controlled in a magneticfield. The second has students design and test a "magnetic bottle."A participant handout (including worksheets) and facilitator notes are made available for download in DOC file format. A link to a required calculator program is also provided.

In this paper, the domain wall (DW) nucleation time and the DW nucleation probability of field-coupled magnets with perpendicular magneticanisotropy are measured by experiment. A well-established Arrhenius model based on thermally activated magnetization reversal is applied to describe the time-dependent DW nucleation probability. Magneto-optical microscopy(MOKE) is used in the experiments to determine the DW nucleation time and the DW nucleation probability in a pNML inverter structure. The DW propagation speed is measured in order to calculate the required DW propagation time for entire magnetization reversal of pNML logic gates. Experimental results are compared to the derived model. Our results show that the interaction in pNML logic gates plays a significant role for the time-dependent DW nucleation probability and therefore for the reliability of field-coupled circuits.

Magnetic properties (Curie temperature, magnetization, magneticanisotropy and rotational hysteresis loss) of Co 100- xCr x films (18 ? x ? 22) and bulk alloys (0 ? × ? 24) were measured to make clear the origin of the perpendicular magneticanisotropy in Co-Cr films. The magnetization, magneticanisotropy and rotational hysteresis loss in films are discussed by taking account of the dispersion of the magneticanisotropy due to a microscopic compositional inhomogeneity. The rotational hysteresis loss of bubble materials such as YFeO 3 and Sm 0.4Y 2.6Fe 3.8Ga 1.2O 12 are also investigated and compared with that of the Co-Cr film.

Understanding the physical properties of magnetic nanowires (NWs) is of crucial importance due to their potential technological applications. In this paper we report a detailed study on the temperature dependence of the magnetic [M(T)] and magnetotransport [MR(T)] properties of Ni and NiFe NWs grown on anodic aluminum oxide templates. While the behavior of the NiFe NWs reflected the presence of a strong shape anisotropy, Ni NWs showed anomalous M(T) and MR(T). The deviations from the expected M(T) and MR(T) behaviors suggest a reorientation of the magnetization easy axis with decreasing temperature. We then extracted the temperature variation of the angle between the magnetization and the NW longitudinal axis, and found an increase from 0? at 370 K to 43? at 5 K. Using a fourth-order magneticanisotropy energy model we were able to successfully explain our results and show that the presence of a magnetoelastic anisotropy contribution due to the compressive stress acting in the NWs is the main origin of the observed magnetization reorientation.

Magneticfields are a major agent in the interstellar medium. They contribute significantly to the total pressure which balances the gas disk against gravitation. They affect the gas flows in spiral arms (Gómez and Cox, 2002). The effective sound speed of the gas is increased by the presence of strong fields which reduce the shock strength. The interstellar fields are closely connected to gas clouds. They affect the dynamics of the gas clouds (Elmegreen, 1981; de Avillez and Breitschwerdt, 2004). The stability and evolution of gas clouds are also influenced by magneticfields, but it is not understood how (Crutcher, 1999; see Chap. 7). Magneticfields are essential for the onset of star formation as they enable the removal of angular momentum from the protostellar cloud during its collapse (magnetic braking, Mouschovias, 1990). Strong fields may shift the stellar mass spectrum towards the more massive stars (Mestel, 1990). MHD turbulence distributes energy from supernova explosions within the ISM (Subramanian, 1998) and regenerates the field via the dynamo process (Wielebinski, R., Krause, 1993, Beck et al., 1996; Sect. 6). Magnetic reconnection is a possible heating source for the ISM and halo gas (Birk et al., 1998). Magneticfields also control the density and distribution of cosmic rays in the ISM. A realistic model for any process in the ISM needs basic information about the magneticfield which has to be provided by observations.

Voyager spacecraft observations have revealed that contrary to expectations, the source of anomalous cosmic rays (ACRs) is not at the local termination shock. A possible mechanism of ACR acceleration is magnetic reconnection in the heliosheath. Using a particle-in-cell code, we investigate the effects of {beta} on reconnection-driven particle acceleration by studying island growth in multiple interacting Harris current sheets. Many islands are generated, and particles are dominantly heated through Fermi reflection in contracting islands during island growth and merging. There is a striking difference between the heating of electrons versus the heating of ions. There is a strong dependence of {beta} on electron heating, while the ion heating is insensitive to {beta}. Anisotropies develop with T {sub Parallel-To} {ne} T for both electrons and ions. The electron anisotropies support the development of a Weibel instability that suppresses the Fermi acceleration of the electrons. Since the Weibel instability develops at a larger T {sub Parallel-To }/T in lower {beta} systems, electrons are able to accelerate more efficiently by the Fermi mechanism at low {beta}. The variance in anisotropy implies less electron acceleration in higher {beta} systems, and thus less heating. This study sheds light on particle acceleration mechanisms within the sectored magneticfield regions of the heliosheath and the dissipation of turbulence such as that produced by the magnetorotational instability in accreting systems.

We present detailed investigations on single crystals of quaternary EuRhAl4Si2 and EuIrAl4Si2. The two compounds order antiferromagnetically at TN1?=?11.7 and 14.7?K, respectively, each undergoing two magnetic transitions. The magnetic properties in the ordered state present a large anisotropy despite Eu2+being an S-state ion for which the single-ion anisotropy is expected to be weak. Two features in the magnetization measured along the c-axis are prominent. At 1.8?K, a ferromagnetic-like jump occurs at very low field to a value one third of the saturation magnetization (1/3?M0) followed by a wide plateau up to 2 T for Rh and 4 T for Ir-compound. At this field value, a sharp hysteretic spin-flop transition occurs to a fully saturated state (M0). Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet. Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis. This suggests that the zero fieldmagnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an up-up-down magnetic structure in zero field. PMID:26156410

This web page, authored and curated by David P. Stern, provides information and a graphical exercise for students regarding the interaction between magneticfield lines and a plasma. The activity involves tracing a typical interplanetary magneticfield line, dragged out of a location on the Sun by the radial flow of the solar wind. This illustrates the way magneticfield lines are "frozen to the plasma" and the wrapping of field lines due to the rotation of the sun. This is part of the work "The Exploration of the Earth's Magnetosphere". A Spanish translation is available.

Spin rectification in a single crystal Fe/Au/Fe sandwich is electrically detected for collinear and noncollinear magnetization and external magneticfield configurations. The line shape, linewidth, and signal polarity are analyzed. The spin rectification theory has been much extended by taking the magnetocrystalline anisotropy and shape anisotropy into account, which explains noncollinear resonances and agrees very well with experimental data. Thus, a comprehensive understanding of spin rectification in ferromagnetic metal is demonstrated in this work.

This letter investigates the effects of in-plane magneticanisotropy on the current induced motion of magnetic domain walls in systems with dominant perpendicular magneticanisotropy, where accumulated spins from the spin Hall effect in an adjacent heavy metal layer are responsible for driving the domain wall motion. It is found that that the sign and magnitude of the domain wall velocity in the uniform flow regime can be tuned significantly by the in-plane magneticanisotropy. These effects are sensitive to the ratio of the adiabatic and non-adiabatic spin transfer torque parameters and are robust in the presence of pinning and thermal fluctuations.

The magnetocrystalline anisotropy (MCA) for an Fe monolayer on MgO substrate (Fe\\/MgO) and that sandwiched by MgO (MgO\\/Fe\\/MgO) is investigated by means of the first principles full-potential linearized augmented plane-wave method, and the effects of an external electric field on the MCA is discussed. In both systems, the MCA is found to be modified through a change in the d

The magneticfield of the sun extends outward through the photosphere into the corona. The resulting coronal and interplanetary magneticfields therefore respond to and evolve with the solar cycle, as well as on shorter and longer time scales. These fields are modeled using photospheric magneticfield observations under the assumption that the coronal field is current free, becomes radial at a 'source surface' placed at 2.5 solar radii from the center of the sun, and is passively advected by the solar wind beyond the source surface. This review covers the computation of such models and their applications to characterize the morphology, evolution, and rotation of coronal and interplanetary magneticfields using data collected between 1976 and the present at the Wilcox Solar Observatory.

Particle-crosslinked polymer composites and gels have recently been shown to possess novel or improved properties due to a covalent particle-matrix interaction. We employ spindle-like hematite particles as exclusive crosslinkers in poly(acrylamide) gels, and exploit their extraordinary magnetic properties for the realization of ferrohydrogels with a perpendicular orientation of the preferred magnetic and geometric axes of the particles. The angle-dependent magnetic properties of uniaxially oriented gels are investigated and interpreted with respect to particle-matrix interactions. The impact of the particle orientation on the resulting angle-dependent magnetic performance reveals the presence of two different contributions to the magnetization: a hysteretic component ascribed to immobilized particles, and a pseudo-superparamagnetic, non-hysteretic component due to residual particle mobility. Furthermore, a plastic reorientation of magnetic particles in the matrix when subjected to a transversal field component is observed. PMID:25423114

We develop an electron theory for the t{sub 2g} electrons of Co{sup 2+} ions to clarify the perpendicular magneticanisotropy (PMA) mechanism of Co-ferrite thin films by considering the spin-orbit interaction (SOI) and crystal-field (CF) potentials induced by the local symmetry around the Co ions and the global tetragonal symmetry of the film. Uniaxial and in-plane MA constants K{sub u} and K{sub 1} at 0 K, respectively, are calculated for various values of SOI and CF. We show that reasonable parameter values explain the observed PMA and that the orbital moment for the in-plane magnetization reduces to nearly half of that of the out-of-plane magnetization.

The magnetic domain structure is a specific property of ferromagnetic materials influencing their main magnetic properties. The aim of this work was to determine a relationship between nanocrystalline and the domain structure observed by means of magneto-optic Kerr effect on the surface of the Fe14.7Co58.8Cu1Nb3Si13.5B9 and Fe13.8Co65Cu0.6Nb2.6Si9B9 toroidal cores, and the induced transverse magneticanisotropy Ku. The transverse magneticanisotropy was induced in the Fe14.7Co58.8Cu1Nb3Si13.5B9 and Fe13.8Co65Cu0.6Nb2.6Si9B9 amorphous cores by annealing them at the temperature of 460 °C, under an external magneticfield of 500 kA/m. It was found that the appearance of nanocrystalline phase in the Fe13.8Co65Cu0.6Nb2.6Si9B9 alloy resulted in considerable increase of the magneticanisotropy constant to 900 J/m3 already after 40 minutes of heating, whereas the nanocrystallization process in the Fe14.7Co58.8Cu1Nb3Si13.5B9 alloy proceeded much slower (after 240 minutes of heating the content of nanocrystalline phase was at the level of about 18%, and the induced magneticanisotropy constant reached 190 J/m3). Observations of the domain structure were also made showing that the 180° domains were obtained in the Fe14.7Co58.8Cu1Nb3Si13.5B9 alloy only after 240 min of heating, whereas similar structure was observed in the Fe13.8Co65Cu0.6Nb2.6Si9B9 alloy already after 40 min of treatment.

In this study, magnetization reversal of a Co-Cr very thin film with rectangular area of 1.0×1.0 cm2 was observed by means of the anomalous Hall effect. The amplitude of the Hall voltage VH took the maximum and minimum values when magneticfield was applied perpendicular and parallel to the film plane, respectively. The hysteresis loop observed in perpendicular direction exhibited the largest lean for the film deposited at substrate temperature Ts of 100 °C. It was found that for the film with a large perpendicular magneticanisotropy constant, VH is independent to the angle of applied field. The Hall loop of the Co-Cr film 150 Å thick revealed its shape more similar to a Kerr loop than a vibrating sample magnetometer loop. The VH-H measurement is useful to evaluate the magnetization process of very thin films without the perturbation of the magnetization component from the substrates and the specimen folder in the measurement system especially for the case of obliquely applied magneticfield condition.

Anisotropic and isotropic Sm{sub 2}Co{sub 17}-type permanent magnets have been prepared by using the conventional sintering technique. Transmission electron microscopy was used to characterize the cellular structure within the Sm{sub 2}(Fe,Co){sub 17} grains. Hysteresis loops (M{approximately}H) were measured in the temperature range from 4.2 to about 1000 K by using a pulsed-field magnetometer with a maximum field strength up to 24 MA/m. The magnetocrystalline anisotropyfield H{sub A} has been measured up to 1000 K by using the singular point detection technique on anisotropic samples with external fields applied perpendicular to the magnetic alignment direction. The saturation magnetization M{sub s} has been measured on anisotropic samples with external fields applied parallel to the magnetic alignment direction. From studies of the coercivity mechanism by using a micromagnetic analysis of the temperature dependence of the coercivity field, it follows that the coercivity of Sm(Co,Fe,Cu,Zr){sub z} is controlled at elevated temperature (above 520 K) by a nucleation process of reversal domains. {copyright} {ital 1997 American Institute of Physics.}

Possible mechanisms of reversing magnetization using stress-induced anisotropy are studied by numerical simulation. A magnetostrictive film with 4-fold magnetocrystalline anisotropy is proposed as a candidate with which full reversal can be performed by a cycle of uniaxial stress\\/strain introduced along a fixed direction in the film plane. Another possibility of stress-driven magnetization reversal is also proposed utilizing precession of magnetization

The magnetic-field characteristics in spiral galaxies are investigated, with emphasis on the Milky Way. The dynamo theory is considered, and axisymmetric spiral (ASS) and bisymmetric spiral (BSS) magneticfields are analyzed. Toroidal and poloidal magneticfields are discussed.

We report dc magnetization measurements on the first available HgBa2CuO4+? and HgBa2Ca2Cu3O8+? (respectively Hg1201 and Hg1223) superconducting single crystals, for fields applied both perpendicular and parallel to the CuO2 planes. In the regime where the magnetization is reversible and linear in logarithm of the applied field, we have used the 3D London theory to determine the penetration depth ? ab for in-plane currents (? ab (0)?1300±100Å, for Hg1201 and ?1500±100 A for Hg1223). Using a relation derived from the anisotropic Ginzburg-Landau approach, we have made an estimate of the anisotropy factor (??30 for Hg1201 and ??50 for Hg1223). The results are in agreement with recent torque experiments on Hg1223.

Thin ferromagnetic films with in-plane magneticanisotropy are promising materials for obtaining high microwave permeability. The paper reports a Mössbauer study of the field induced in-plane uniaxial anisotropy in electro-deposited FeCo alloy films. The FeCo alloy films were prepared by the electro-deposition method with and without an external magneticfield applied parallel to the film plane during deposition. Vibrating sample magnetometry and Mössbauer spectroscopy measurements at room temperature indicate that the film deposited in external field shows an in-plane uniaxial anisotropy with an easy direction coinciding with the external field direction and a hard direction perpendicular to the field direction, whereas the film deposited without external field does not show any in-plane anisotropy. Mössbauer spectra taken in three geometric arrangements show that the magnetic moments are almost constrained in the film plane for the film deposited with applied magneticfield. Also, the magnetic moments tend to align in the direction of the applied external magneticfield during deposition, indicating that the observed anisotropy should be attributed to directional ordering of atomic pairs.

Asymmetries in exoplanet transits are proving to be a useful tool for furthering our understanding of magnetic activity on both stars and planets outside our Solar System.Near-UV observations of the WASP-12 system have revealed asymmetries in the timing of the transit when compared with the optical light curve. A number of possible explanations have been suggested for this variation, including the presence of a magnetospheric bow shock arising from the interaction of the planet's magneticfield with the stellar wind from it's host star. Such observations provide the first method for directly detecting the presence of a magneticfield on exoplanets.The shape and size of such asymmetries is highly dependent on the structure of the host stars magneticfield at the time of observation. This implies we may observe highly varying near-UV transit light curves for the same system. These variations can then be used to learn about the geometry of the host star's magneticfield.In this presentation I will show modelling a bow shock around an exoplanet can help us to not only detect, but also also place constraints on the magneticfield strength of hot Jupiters. For some systems, such as HD 189733, we have maps of the surface magneticfield of the star at various epochs. I will also show how incorporating these maps into a stellar wind model, I can model the formation of a bow shock around the planet and hence demonstrate the variability of the near-UV transits.

We calculate the number density, energy density, transverse pressure, longitudinal pressure, and magnetization of an ensemble of spin one-half particles in the presence of a homogenous background magneticfield. The magneticfield direction breaks spherical symmetry causing the pressure transverse to the magneticfield direction to be different than the pressure parallel to it. We present explicit formulas appropriate at zero and finite temperature for both charged and uncharged particles including the effect of the anomalous magnetic moment. We demonstrate that the resulting expressions satisfy the canonical relations ?=-P? and P?=P?-MB, with M=-??/?B being the magnetization of the system. We numerically calculate the resulting pressure anisotropy for a gas of protons and a gas of neutrons and demonstrate that the inclusion of the anomalous magnetic increases the level of pressure anisotropy in both cases.

We evaluate the fluxes measured by the magnetic flux loops installed in LHD by using a three dimensional MHD equilibrium analysis code, ANIMEC, which enable us to directly determine the calibration function between the anisotropic pressure and the measured fluxes for the non-axisymmetric plasmas for the first time. The result indicates that the diamagnetic flux represents a nearly single-valued function of the beta perpendicular with respect to the field, and the saddle loop flux represents a nearly single-valued function of an equally weighted average of the beta values parallel and perpendicular to the field, regardless of the pressure anisotropy or the amount of energetic trapped particles. The values of the beta perpendicular to the field and the equal weighting averaged beta estimated by the single-valued functions (calibration functions) are investigated in order to clarify the magnitude of deviation from those original values, and the range of anisotropy where the beta value evaluated by the magnetic flux measurement is calculated within a 10% error.

When charged particles move in a random magneticfield superimposed upon a relatively large constant field, their pitch angle distribution can be calculated to any desired precision by an iterative approximation procedure. Improved knowledge of the pitch angle distribution and of the characteristic time for relaxation of anisotropy leads to an accurate expression for the coefficient of diffusion parallel to the mean field.

In exhibiting the coercivity of permanent magnets, magnetocrystalline anisotropy plays an important role. Since itinerant magnetic states are responsible to direct interactions among magnetic sites, d states are expected to be sensitive to lattice strain. In this work, we report strain effects on magnetic properties theoretically studied by first-principles calculations for Y2Fe14B, where Y is a prototypical f0 rare-earth element. To analyze the local magneticanisotropy, we developed a method to decompose the magnetic-anisotropy energy into contribution from each atomic site as well as from couplings among specific atomic orbitals, where the sum rule is satisfied by including indirect off-site contributions in the second-order perturbation. The OpenMX code is used for first-principles calculations. The lattice constants of Y2Fe14B are changed from the equilibrium values independently, where we found the uniform compression enhances the perpendicular magneticanisotropy. Our magnetic-anisotropy decomposition identified dominant magnetic site and orbital couplings. Our method will enable us to study the anisotropy at microstructure interfaces. This work was supported by ESICMM and the K computer.

This is an activity about electromagnetism. Learners will use a compass to map the magneticfield lines surrounding a coil of wire that is connected to a battery. This activity requires a large coil or spool of wire, a source of electricity such as 3 D-cell batteries or an AC to DC power adapter, alligator-clipped wire, and magnetic compasses. This is the third lesson in the second session of the Exploring Magnetism teachers guide.

The {delta}N formula for the primordial curvature perturbation {zeta} is extended to include vector as well as scalar fields. Formulas for the tree-level contributions to the spectrum and bispectrum of {zeta} are given, exhibiting statistical anisotropy. The one-loop contribution to the spectrum of {zeta} is also worked out. We then consider the generation of vector field perturbations from the vacuum, including the longitudinal component that will be present if there is no gauge invariance. Finally, the {delta}N formula is applied to the vector curvaton and vector inflation models with the tensor perturbation also evaluated in the latter case.

Using DC and AC magnetometry, the pressure dependence of the magnetization of the threedimensional antiferromagnetic coordination polymer Mn(N(CN)2)2 was studied up to 12 kbar and down to 8 K. The magnetic transition temperature, Tc, increases dramatically with applied pressure (P), where a change from Tc(P = ambient) = 16:0 K to Tc(P = 12:1 kbar) = 23:5 K was observed. In addition, a marked difference in the magnetic behavior is observed above and below 7.1 kbar. Specifically, for P < 7:1 kbar, the differences between the field-cooled and zero-field-cooled (fc-zfc) magnetizations, the coercive field, and the remanent magnetization decrease with increasing pressure. However, for P > 7:1 kbar, the behavior is inverted. Additionally, for P > 8:6 kbar, minor hysteresis loops are observed. All of these effects are evidence of the increase of the superexchange interaction and the appearance of an enhanced exchange anisotropy with applied pressure.

We present an investigation of the large magneticanisotropy of Fe2P, based on ab initio density functional theory calculations, with a full-potential linear muffin-tin orbital basis. We obtain a uniaxial magneticanisotropy energy (MAE) of 664 ?eV/f.u., which is in decent agreement with experimental observations. Based on a band structure analysis the microscopic origin of the large magneticanisotropy is explained. We also show that by straining the crystal structure, the MAE can be enhanced further.

In recent years there has been increased concern over potential health hazards related to exposure of personnel to magneticfields. If exposure standards are to be established, then a means for measuring magneticfield dose must be available. To meet this need, the Department of Energy has funded development of prototype dosimeters at the Battelle Pacific Northwest Laboratory. This manual reviews the principle of operation of the dosimeter and also contains step-by-step instructions for its operation.

An antiferromagnet-ferromagnet-antiferromagnet trilayer was grown in magneticfield using CoMn, permalloy (Py), and FeMn, respectively. Magnetometry studies show that the direction of exchange coupling of CoMn with Py was perpendicular to that of Py with FeMn. These results are explained by a spin flop in the CoMn layer and show that the spin structure of an antiferromagnet may undergo severe modification due to a relatively small magneticfield applied during its growth. The perpendicular exchange coupling was exploited in the CoMn-Py-FeMn trilayer to manipulate the easy axis of the ferromagnet.

The theoretical prediction, by Ivanov and Kosevich, of ``magnon drop'' solitons in thin films with perpendicular magneticanisotropy (PMA) and zero damping, dates back to the 1970s. More recently, Hoefer, Silva and Keller, demonstrated analytically and numerically that related ``magnetic droplet'' solitons should be possible to excite in nano-contact spin-torque oscillators (NC-STOs) based on PMA materials, where spin transfer torque locally realizes the zero-damping condition required in. In my talk, I will present the first experimental demonstration of such magnetic droplets, realized using 50-100 nm diameter nano-contacts (NCs) fabricated on top of orthogonal GMR stacks of Co8/Cu/Co0.3[Ni0.8/Co0.4]x4 (thicknesses in nm). The nucleation of a magnetic droplet manifests itself as a dramatic 10 GHz drop in microwave signal frequency at a drive-current dependent critical perpendicular field of the order of 0.5 - 1 T. The drop in frequency is accompanied by a simultaneous sharp resistance increase of the device and a sign change of its magnetoresistance, directly indicating the existence of a reversed magnetization in a region of the [Co/Ni] free layer underneath the NC. As predicted by numerical simulations the droplet exhibits rich magnetodynamic properties, experimentally observed as auto-modulation at approximately 1 GHz and sometimes sidebands at 1/2 and 3/2 of the fundamental droplet frequency. The 1 GHz modulation can be shown numerically to be related to the drift instability of the droplet, albeit with enough restoring force to make the droplet perform a periodic motion instead of leaving the NC region. The sidebands at 1/2 and 3/2 the droplet frequency are related to eigenmodes of the droplet perimeter. Magnetic droplet nucleation is found to be robust and reproducible over a wide number of NC-STOs with different NC sizes, making this new nanomagnetic object as fundamental and potentially useful to nanomagnetism as e.g. domain walls and vortices. The theoretical prediction, by Ivanov and Kosevich, of ``magnon drop'' solitons in thin films with perpendicular magneticanisotropy (PMA) and zero damping, dates back to the 1970s. More recently, Hoefer, Silva and Keller, demonstrated analytically and numerically that related ``magnetic droplet'' solitons should be possible to excite in nano-contact spin-torque oscillators (NC-STOs) based on PMA materials, where spin transfer torque locally realizes the zero-damping condition required in. In my talk, I will present the first experimental demonstration of such magnetic droplets, realized using 50-100 nm diameter nano-contacts (NCs) fabricated on top of orthogonal GMR stacks of Co8/Cu/Co0.3[Ni0.8/Co0.4]x4 (thicknesses in nm). The nucleation of a magnetic droplet manifests itself as a dramatic 10 GHz drop in microwave signal frequency at a drive-current dependent critical perpendicular field of the order of 0.5 - 1 T. The drop in frequency is accompanied by a simultaneous sharp resistance increase of the device and a sign change of its magnetoresistance, directly indicating the existence of a reversed magnetization in a region of the [Co/Ni] free layer underneath the NC. As predicted by numerical simulations the droplet exhibits rich magnetodynamic properties, experimentally observed as auto-modulation at approximately 1 GHz and sometimes sidebands at 1/2 and 3/2 of the fundamental droplet frequency. The 1 GHz modulation can be shown numerically to be related to the drift instability of the droplet, albeit with enough restoring force to make the droplet perform a periodic motion instead of leaving the NC region. The sidebands at 1/2 and 3/2 the droplet frequency are related to eigenmodes of the droplet perimeter. Magnetic droplet nucleation is found to be robust and reproducible over a wide number of NC-STOs with different NC sizes, making this new nanomagnetic object as fundamental and potentially useful to nanomagnetism as e.g. domain walls and vortices. Support from The Swedish Foundation for Strategic Research, The Swedish Research Council, and the Knut and Alice Walle

The relation between thickness and domain structure of Co80Pt20 perpendicular magneticanisotropy films was investigated through experiments and micromagnetic simulation. The films with thickness over 10 nm exhibited clear maze domain structure, while for the films thinner than 10 nm the domain structure abruptly changed from maze domain to irregular and large domain as the thickness became thinner. The irregular domain had narrower domain wall width than maze domain.

Ordered CoNiP nanowires with the same length of 4 µm and varying diameters (d = 100 nm600 nm) were fabricated by electrodeposition of CoNiP onto polycarbonate templates. X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy confirmed the quality of the fabricated nanowires. Magnetic measurements and theoretical analysis revealed that the magnetization reversal and magneticanisotropy were significantly influenced by varying of the diameters of the nanowires. There existed a critical wire diameter (dc ? 276 nm), below which the magnetization reversal occurred via a coherent rotation mode, and above which the magnetization reversal occurred via a curling rotation mode. The easy axis of the magnetization tended to change in direction from parallel to perpendicular with respect to the wire axis as the wire diameter exceeded dc ? 276 nm. With increasing wire diameter, the coercive field (Hc) and the remanent to saturation magnetization ratio (Mr/Ms) were also found to rapidly decrease in the range d = 100400 nm and gradually decrease for d > 400 nm. PMID:25760054

Magnetic and magneto-transport properties of amorphous Al2O3-based magnetic tunnel junctions (MTJ) having two Co/Ni multilayer electrodes exhibiting perpendicular magneticanisotropy (PMA) are presented. An additional Co/Pt multilayer is required to maintain PMA in the top Co/Ni electrode. Slight stacking variations lead to dramatic magnetic changes due to dipolar interactions between the top and bottom electrodes. Tunnel magneto-resistance (TMR) of up to 8% at 300 K is measured for the MTJ with two PMA electrodes. The TMR value increases when the top PMA electrode is replaced by an in-plane magnetized Co layer. These observations can be attributed to significant intermixing in the top Co/Ni electrode.

The temperature dependence of Co anisotropy on a nano-FeOx layer was studied in the structure of IrMn/Co (FM1)/FeOx/Co (FM2). An anisotropy transition of the FM2 was observed from a combination of uniaxial and unidirectional anisotropies at room temperature (RT) to unidirectional anisotropy at temperature below 80 K through field cooling process. Various ferromagnetic (FM) and antiferromagnetic (AFM) components existing in the FeOx layer were attributable to the observed anisotropy of FM2. AFM domains with TN higher than room temperature were responsible for the observed uniaxial anisotropy at RT and AFM domains with TN of 80 K were accountable for the anisotropy transition, below which the unidirectional anisotropy became dominant. In addition, the direction of the shifted loop could be determined by the cooling field direction.

Measurements of the magnetization were performed between 4.2 and 300 K on a series of periodically stacked layers of cerium hydride and cobalt prepared by reactive ion-beam sputtering. X-ray reflectometry shows that the interfaces are sharp with a rms roughness of nominally one atomic layer. In the ground state at low temperatures, for Co-layer thicknesses up to 17 Å, the magnetization is spontaneously oriented perpendicular to the layer planes in a multidomain configuration. A phenomenological analysis of the measured magneticanisotropy energy reveals that the out-of-plane orientation of the magnetic easy axis is the result of a strong interface anisotropy which overcomes the shape anisotropy of the Co layers and of an additional volume anisotropy. Possible mechanisms behind the surface and volume anisotropies are discussed. Between 50 and 100 K, the magnetization turns into the layer planes in a continuous transition. The saturation magnetization, the spin-wave parameter describing its temperature dependence and the anisotropy energy vary continuously through the transition from the crystalline fcc phase to the amorphous phase of the Co sublayers near 20 Å. This reveals the close relationship between the electronic configurations of amorphous and fcc Co. The magnetization measurements are supplemented by measurements of the anisotropic magnetoresistance and the extraordinary Hall effect. The extraordinary Hall coefficient shows contributions from skew scattering and side jump processes and scales with the ordinary electrical resistivity.

Measurements of the magnetization were performed between 4.2 and 300 K on a series of periodically stacked layers of cerium hydride and cobalt prepared by reactive ion-beam sputtering. X-ray reflectometry shows that the interfaces are sharp with a rms roughness of nominally one atomic layer. In the ground state at low temperatures, for Co-layer thicknesses up to 17 {Angstrom}, the magnetization is spontaneously oriented perpendicular to the layer planes in a multidomain configuration. A phenomenological analysis of the measured magneticanisotropy energy reveals that the out-of-plane orientation of the magnetic easy axis is the result of a strong interface anisotropy which overcomes the shape anisotropy of the Co layers and of an additional volume anisotropy. Possible mechanisms behind the surface and volume anisotropies are discussed. Between 50 and 100 K, the magnetization turns into the layer planes in a continuous transition. The saturation magnetization, the spin-wave parameter describing its temperature dependence and the anisotropy energy vary continuously through the transition from the crystalline fcc phase to the amorphous phase of the Co sublayers near 20 {Angstrom}. This reveals the close relationship between the electronic configurations of amorphous and fcc Co. The magnetization measurements are supplemented by measurements of the anisotropic magnetoresistance and the extraordinary Hall effect. The extraordinary Hall coefficient shows contributions from skew scattering and side jump processes and scales with the ordinary electrical resistivity. {copyright} {ital 1997} {ital The American Physical Society}

The magnetocrystalline anisotropy constant K1 of iron was determined from static torque measurements on a {001} single-crystal disk at fields between 3000 and 18 000 Oe, and at temperatures between 77 and 900°K. It was found that (i) (?K1?T)K1~=10(?M?T)M above 300°K, in agreement with Zener; (ii) (?K1?H)K1~=22(?M?H)M below 600°K, and at H~=10 KOe; and (iii) (?K1?H)(?K1?T)~=- 1.25×10-3°K\\/Oe over the whole

A cross section of a circular wire loop carrying an unknown current is shown above. The arrows represent the direction of the magneticfield. The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black. You can double-click in the animation to add magneticfield lines, click-drag the center of the loop to reposition it, and click-drag the top or bottom of the loop to change its size.

We studied the magnetic and elastic wave speed anisotropy of a synthetically prepared quartz-mica schist, prior to, during and after experimental melting. The synthetic rock was manufactured from a mixture of powders with equal volumes of quartz and muscovite. The powders were initially compacted with 200 MPa uniaxial stress at room temperature and sealed in a stainless steel canister. Subsequently the sealed canister was isostatically pressed at 180 MPa and 580 °C for 24 hours. This produced a solid medium with ~25 % porosity. Mica developed a preferred grain-shape alignment due to the initial compaction with differential load, where mica flakes tend to orient perpendicular to the applied stress and hence define a synthetic foliation plane. In the last stage we used a Paterson gas-medium apparatus, to pressurize and heat the specimens up to 300 MPa and 750 °C for a six hour duration. This stage initially compacted the rock, followed by generation of melt, and finally crystallization of new minerals from the melt. Elastic wave speed measurements were performed in situ at pressure and temperature, with a transducer assembly mounted next to the sample. Magnetic measurements were performed before and after the partial melt experiments. Anisotropy was measured in low- and high-field, using a susceptibility bridge and torsion magnetometer, respectively. Additionally we performed measurements of hysteresis, isothermal remanent magnetization (IRM) and susceptibility as a function of temperature, to investigate the magnetic properties of the rock. The elastic wave speed, before the melting-stage of the experiment, exhibits a distinct anisotropy with velocities parallel to the foliation being about 15 % higher than normal to the foliation plane. Measurements of the magneticanisotropy in the bulk sample show that anisotropy is originating from the preferred orientation of muscovite, with a prominent flattening fabric. In contrast, specimens that underwent partial melting display a weaker elastic and magneticanisotropy, because muscovite preferentially melts due to dehydration melting at 750 °C. The decrease in anisotropy can be inferred from in situ observation of elastic wave anisotropy, but also from comparison of measurements of magneticanisotropy prior to and subsequent to experiment. A distinct anisotropy is however identified after the experiments both in susceptibility and remanence, which appears to be controlled by the original foliation. As muscovite undergoes dehydration melting a small amount of Fe is released into the melt. Crystallization from the melt indicates that the Fe is bound in biotite and Fe-oxides. The bulk susceptibility and saturation remanence increase by more than one order of magnitude in samples after the melting experiment. The newly formed ferrimagnetic phase, identified through hysteresis, IRM and thermomagnetic measurements, have a tight grouping in the magnetite pseudo-single-domain field on a Day plot. Our experiments are pertinent to the study of partially molten rocks and provide an opportunity to help guide research in magnetic and elastic wave anisotropy of migmatite and granite. In particular the results from experiments apply to the understanding of generation and percolation of melt prior to, or coeval to, the onset of deformation.

This article surveys three major areas of biomagnetic research: (a) the magneto-orientation effect; (b) the role of the geomagnetic field in bird orientation and navigation; and (c) the biological effects of extremely low-frequency magneticfields. The magneto-orientation effect is caused by diamagnetic anisotropy of highly ordered biological structures, such as visual photoreceptor and chloroplast membranes, in a homogeneous magneticfield

We investigate the spectral shape, the anisotropy of the wave vector distributions and the anisotropy of the amplitudes of the magnetic fluctuations in the Earth's magnetosheath within a broad range of frequencies [10-3, 10] Hz which corresponds to spatial scales from ~10 to 105 km. We present the first observations of a Kolmogorov-like inertial range of Alfvénic fluctuations ?B2⊥}~f-5/3 in the magnetosheath flanks, below the ion cyclotron frequency fci. In the vicinity of fci, a spectral break is observed, like in solar wind turbulence. Above the break, the energy of compressive and Alfvénic fluctuations generally follows a power law with a spectral index between -3 and -2. Concerning the anisotropy of the wave vector distribution, we observe a clear change in its nature in the vicinity of ion characteristic scales: if at MHD scales there is no evidence for a dominance of a slab (k?>>k⊥) or 2-D (k⊥>>k?) turbulence, above the spectral break, (f>fci, kc/?pi>1) the 2-D turbulence dominates. This 2-D turbulence is observed in six selected one-hour intervals among which the average ion ? varies from 0.8 to 10. It is observed for both the transverse and compressive magnetic fluctuations, independently on the presence of linearly unstable modes at low frequencies or Alfvén vortices at the spectral break. We then analyse the anisotropy of the magnetic fluctuations in a time dependent reference frame based on the field B and the flow velocity V directions. Within the range of the 2-D turbulence, at scales [1,30]kc/?pi, and for any ? we find that the magnetic fluctuations at a given frequency in the plane perpendicular to B have more energy along the B×V direction. This non-gyrotropy of the fluctuations at a fixed frequency is consistent with gyrotropic fluctuations at a given wave vector, with k⊥>>k?, which suffer a different Doppler shift along and perpendicular to V in the plane perpendicular to B.

The magnetization reversal processes of a 150 Å thick epitaxial Fe/GaAs(001) film are modified by controlling the lateral dimensions of the continuous film to create rectangular microstripes of constant length and varying width. Size dependent transitions from (a) two-jump to single-jump, and (b) single-jump to two-jump reversal processes are observed for magnetization reversal along the two mutually perpendicular cubic easy axes (parallel and perpendicular to the easy axis of the shape anisotropy, respectively). This behavior can be explained by a simple model of the effective anisotropy energy contributions including the shape anisotropy energy.

Frequency shift of gradient-echo MRI provides valuable information for assessing brain tissues. Recent studies suggest that the frequency and susceptibility contrast depend on white matter fiber orientation. However, the molecular underpinning of the orientation dependence is unclear. In this study, we investigated the orientation dependence of susceptibility of human brain in vivo and mouse brains ex vivo. The source of susceptibility anisotropy in white matter is likely to be myelin as evidenced by the loss of anisotropy in the dysmyelinating shiverer mouse brain. A biophysical model is developed to investigate the effect of the molecular susceptibility anisotropy of myelin components, especially myelin lipids, on the bulk anisotropy observed by MRI. This model provides a consistent interpretation of the orientation dependence of macroscopic magnetic susceptibility in normal mouse brain ex vivo and human brain in vivo and the microscopic origin of anisotropic susceptibility. It is predicted by the theoretical model and illustrated by the experimental data that the magnetic susceptibility of the white matter is least diamagnetic along the fiber direction. This relationship allows an efficient extraction of fiber orientation using susceptibility tensor imaging. These results suggest that anisotropy on the molecular level can be observed on the macroscopic level when the molecules are aligned in a highly ordered manner. Similar to the utilization of magnetic susceptibility anisotropy in elucidating molecular structures, imaging magnetic susceptibility anisotropy may also provide a useful tool for elucidating the microstructure of ordered biological tissues. PMID:22036681

Diffuse x-ray scattering measurements have been made on ferromagnetic Fe22.5Ni77.5, permalloy, annealed in a 3000 G magneticfield at 450° C. These measurements reveal a long predicted anisotropic alignment of the Fe-Ni, Fe-Fe and Ni-Ni near-neighbor pairs relative to the magneticfield direction when annealed at temperatures below the Curie Temperature but high enough for diffusion to occur. Our direct measurements show that the Fe-Fe and Ni-Ni first neighbor pairs preferentially align along the annealing direction of the magneticfield for fields in the [100], [110] and [111] crystallographic directions. Fe-Ni pairs prefer to align perpendicular to the direction of the applied field. The size of the observed anisotropy in the atom pair distribution follows that observed in their magnetic properties1; the anisotropy increases from [100] to [110] to [111]. This first direct verification that magnetic annealing preferentially aligns the direction of the atomic pairs will be discussed. 1. S. Chikazumi, J. Phys. Soc. Japan 11, 551 (1956).

Expressions describing the energy loss of a charged particle in a Maxwellian plasma with a strong magneticfield are described. The dielectric constant found by means of quantum-mechanical correlation functions is used. The Coulomb logarithm is calculated for strong magneticfields and is found to be a function of the magneticfield. The anisotropy of the energy loss of a

The Helioseismic and Magnetic Imager (HMI) on SDO has measured magneticfield, velocity, and intensity in the photosphere over the full disk continuously since May 2010 with arc-second resolution. Scalar images are measured every 45 seconds. From these basic observables the pipeline automatically identifies and tracks active regions on the solar disk. The vector magneticfield and a variety of summary quantities are determined every 720s in these tracked Space-weather HMI Active Region Patches (SHARPS). Synoptic and synchronic maps are constructed daily and after each Carrington Rotation Most data products are available with definitive scientific calibration after a few day deal at and in a quick-look near-real-time version a few minutes after the observations are made. Uncertainties are determined for the derived products. All of the magneticfield products along with movies and images suitable for browsing are available at http:://Hmi.stanford.edu/magnetic. Other products, e.g. coronal field over active regions, can be computed on demand.

Superparamagnetic beads are widely used in biochemistry and single-molecule biophysics, but the nature of the anisotropy that enables the application of torques remains controversial. To quantitatively investigate the torques experienced by superparamagnetic particles, we use a biological motor to rotate beads in a magneticfield and demonstrate that the underlying potential is ? periodic. In addition, we tether a bead to a single DNA molecule and show that the angular trap stiffness increases nonlinearly with magneticfield strength. Our results indicate that the superparamagnetic beads' anisotropy derives from a nonuniform intrabead distribution of superparamagnetic nanoparticles.

Dipolar interactions in a soft/Pd/hard [CoNi/Pd]{sub 30}/Pd/[Co/Pd]{sub 20} multilayer system, where a thick Pd layer between two ferromagnetic units prevents direct exchange coupling, are directly revealed by combining magnetometry and state-of-the-art layer resolving soft x-ray imaging techniques with sub-100-nm spatial resolution. The domains forming in the soft layer during external magneticfield reversal are found to match the domains previously trapped in the hard layer. The low Curie temperature of the soft layer allows varying its intrinsic parameters via temperature and thus studying the competition with dipolar fields due to the domains in the hard layer. Micromagnetic simulations elucidate the role of [CoNi/Pd] magnetization, exchange, and anisotropy in the duplication process. Finally, thermally driven domain replication in remanence during temperature cycling is demonstrated.

In the multilayer system [Fe/CeH 2]× n a strong interface anisotropy causes a rotation of the magnetization direction out of the layer plane at a temperature TR. Measurements of the 57Fe Mössbauer spectra and of the magnetization curves by the magneto-optical Kerr effect on samples with a different number of bilayers n are presented which reveal that a contribution from the magnetostatic interaction between the domains adds to the interface anisotropy to stabilize the out-of-plane magnetization orientation; with increasing n, TR increases and the angle ? between the average magnetization direction and the layer normal decreases.

The origin and evolution of cosmic magneticfields, their strength and structure in intergalactic space, their first occurrence in young galaxies, and their dynamical importance for galaxy evolution remain widely unknown. Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magneticfields in galaxies. Unpolarized radio synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important; they can affect gas flows and drive gas inflows in central regions. Polarized radio emission traces ordered fields which can be regular or anisotropic turbulent, generated from isotropic turbulent fields by compression or shear. The strongest ordered fields of 10-15 ?G strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. In galaxies with strong density waves, ordered (anisotropic turbulent) fields are also observed at the inner edges of the spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Irregular galaxies host isotropic turbulent fields often of similar strength as in spiral galaxies, but only weak ordered fields. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several galaxies reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by a mean-field ? -? dynamo. So far no indications were found in external galaxies of large-scale field reversals, like the one in the Milky Way. Ordered magneticfields are also observed in radio halos around edge-on galaxies out to large distances from the plane, with X-shaped patterns. In the outflow cone above a starburst region of NGC 253, RM data indicate a helical magneticfield.

We studied surface morphology induced changes of magneticanisotropy, magnetization reversal, and symmetry of the anisotropic magnetoresistance (AMR) in ion sputtered Ni films grown on MgO (001). Grazing-incidence ion sputtering generally develops anisotropic surface roughness of the Ni films, i.e., nanometer wide ripples parallel to the ion beam direction, giving rise to uniaxial magneticanisotropy with the easy axis along the ion beam direction. The formed ripples act as domain wall nucleation and pinning sites during magnetization reversal, while two-jump domain wall motion dominates in the as-grown Ni films. More importantly, the azimuthal angular dependence of the AMR indicates a superposition of twofold symmetry and fourfold symmetry. By relying on grazing-incidence ion sputtering along specific crystallographic directions, we are able to tailor the relative weight of twofold and fourfold symmetry of AMR. We demonstrate that in contrast to the bulk case, the symmetry of the AMR becomes also sensitive to the surface morphology in thin films, which is in particular relevant for the design of magnetotransport based sensors.

In order to better understand the origin of field-induced anisotropy (Ku) in Si-free nanocrystalline soft magnetic alloys, the lattice spacing of the bcc-Fe phase in nanocrystalline Fe94-xNb6Bx (x = 10, 12, 14) alloys annealed under an applied magneticfield has been investigated by X-ray diffraction in transmission geometry (t-XRD) with the diffraction vector parallel and perpendicular to the field direction. The saturation magnetostriction (?s) of nanocrystalline Fe94-xNb6Bx was found to increase linearly with the volume fraction of the residual amorphous phase and is well described by taking into account the volume-weighted average of two local ?s values for the bcc-Fe nanocrystallites (-5 ± 2 ppm) and the residual amorphous matrix (+8 ± 2 ppm). The lattice distortion required to produce the measured Ku values (100 J/m3) was estimated via the inverse magnetostrictive effect using the measured ?s values and was compared to the lattice spacing estimations made by t-XRD. The lattice strain required to produce Ku under the magnetoelastic model was not observed by the t-XRD experiments and so the findings of this study suggest that the origin of magneticfield induced Ku cannot be explained through the magnetoelastic effect.

A series of pentacoordinate Ni(ii) complexes of the general formula [Ni(L5)] () with various pentadentate Schiff base ligands H2L5 (originating in a condensation of aromatic ortho-hydroxy-aldehydes and aliphatic triamines) was synthesized and characterized by X-ray structure analysis and magnetometry. The alternations of substituents on the H2L parent ligand resulted in the complexes with the geometry varying between the square-pyramid and trigonal-bipyramid. In the compounds whose chromophore geometry is closer to a trigonal-bipyramid, a large and negative uniaxial anisotropy (D = -64 cm(-1)) was identified. Moreover, the simple linear expression for the axial zero-field splitting (ZFS) parameter, D/cm(-1) = 32.7(4.8) - 151(10)?, was proposed, where ? (in degrees) stands for the Addison parameter. The results of magnetic analysis were also supported by ab initio CASSCF/NEVPT2 calculations of the ZFS splitting parameters D and E, and g tensors. Despite large and negative D-values of the reported compounds, slow relaxation of magnetization was not observed either in zero or non-zero static magneticfield, thus no single-molecule magnetic behaviour was detected. PMID:25919125

Perpendicular magneticanisotropy (PMA) in thin ferromagnetic films has attracted a great deal of attention due to interesting physics and promising application in spintronic devices. The strength of PMA is often found to be strongly influenced by the adjacent heavy metal layer and oxide layer. A strong interest has emerged recently to control the PMA of these ultra-thin films by electric fields. Here we report the fabrication and characterization of perpendicularly magnetized 3d transitional metal films next to high-k oxides such as HfO2 and ZrO2. We have investigated structural, magnetic and transport properties of these films. The PMA strongly depends on the thickness of the ferromagnetic layers and the interfacial oxidation level of the bilayers. We will also discuss electric field controlled magnetic properties in these systems. This work was supported in part by NSF (ECCS-1310338) and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

The effects of magnetocrystalline anisotropy (Ku) and magnetization saturation (Ms) on the mechanically induced switching in nanomagnets are studied using a constraint-free phase field model, which allows explicit magneto-mechanical coupling and strictly constant magnetization magnitude. The effects of Ku and Ms on the transition boundary between the coherent and incoherent switching modes are presented in terms of the nanomagnet geometry. It is found that Ms rather than Ku can affect the transition boundary between the two switching modes. In the coherent mode, there exists a critical strain ( ?c ) to induce a deterministic 90° switching. By using the dynamic nature and overrun behavior of the magnetization, a deterministic 180° switching can occur if the mechanical strain is removed once the magnetization rotates to the largest achievable angle ( ?1m ). For 90° switching, increasing Ku can enhance both ?c and ?1m , whereas Ms incurs no noticeable changes. For 180° switching, the switching time (ts) increases with Ms linearly, but initially decreases with increasing Ku and then saturates. The results for ts suggest that moderate Ku and Ms are advisable to simultaneously obtain relatively low ?c , quick switching, high storage density, and high magnetization-state stability in nanomagnets. This work provides insight on tuning mechanically assisted nanomagnet-based logic and memory devices through Ms and Ku.

Depth grading of magneticanisotropy in perpendicular magnetic media has been predicted to reduce the field required to write data without sacrificing thermal stability. To study this prediction, we have produced Co\\/Pd multilayers with depth-dependent Co layer thickness. Polarized neutron reflectometry shows that the thickness grading results in a corresponding magneticanisotropy gradient. Magnetometry reveals that the anisotropy gradient promotes

Electromagnets used as beam guiding elements in particle accelerators and colliders require very tight tole-rances on their magneticfields and on their alignment along the particle path. This article describes the methods and equipment used for magnetic measurements in beam transport magnets. Descriptions are given of magnetic resonance techniques, various induction coil methods, Hall generator measurements, the fluxgate magnetometer as

This paper investigates the bipartite entanglement of a two-qubit Heisenberg XXZ chain under an inhomogeneous magneticfield. By the concept of negativity, we find that the inhomogeneity of the magneticfield may induce entanglement and the critical magneticfield is independent of Jz. We also find that the entanglement is symmetric with respect to a zero magneticfield. The anisotropy parameter Jz may enhance the entanglement.

A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

We report ac susceptibility and continuous wave and pulsed EPR experiments performed on GdW10 and GdW30 polyoxometalate clusters, in which a Gd3+ ion is coordinated to different polyoxometalate moieties. Despite the isotropic character of gadolinium as a free ion, these molecules show slow magnetic relaxation at very low temperatures, characteristic of single molecule magnets. For T?200??mK, the spin-lattice relaxation becomes dominated by pure quantum tunneling events, with rates that agree quantitatively with those predicted by the Prokof'ev and Stamp model [Phys. Rev. Lett. 80, 5794 (1998)]. The sign of the magneticanisotropy, the energy level splittings, and the tunneling rates strongly depend on the molecular structure. We argue that GdW30 molecules are also promising spin qubits with a coherence figure of merit Q(M)?50. PMID:23004325

We propose and demonstrate, through simulation, an ultra low energy memory device on a topological insulator thin film. The device consists of a thin layer of Fe deposited on the surface of a topological insulator, Bi2Se3. The top surface of Fe is covered with MgO so that the ferromagnetic layer has perpendicular anisotropy. Current is passed on the surface of the topological insulator which switches the magnetization of the Fe ferromagnet through strong exchange interaction, between electrons contributing to the surface current on the Bi2Se3 and the d electrons in the ferromagnet, and spin transfer torque due to shunting of current through the ferromagnet. Voltage controlled magneticanisotropy enables ultra low energy switching. Our micromagnetic simulations, predict switching time of the order of 2.4 ns and switching energy of the order of 0.16 fJ for a ferromagnetic bit with thermal stability of 90 kBT. The proposed structure combines the advantages of both large spin torque from topological insulators and those of perpendicular anisotropy materials. This work is supported by NRI SWAN and NSF NASCENT Center.

When magnetic nanoparticles (MNPs) are single domain and magnetically independent, their magnetic properties and the conditions to optimize their efficiency in magnetic hyperthermia applications are now well understood. However, the influence of magnetic interactions on magnetic hyperthermia properties is still unclear. Here, we report hyperthermia and high-frequency hysteresis loop measurements on a model system consisting of MNPs with the same size but a varying anisotropy, which is an interesting way to tune the relative strength of magnetic interactions. A clear correlation between the MNP anisotropy and the squareness of their hysteresis loop in colloidal solution is observed: the larger the anisotropy, the smaller the squareness. Since low anisotropy MNPs display a squareness higher than the one of magnetically independent nanoparticles, magnetic interactions enhance their heating power in this case. Hysteresis loop calculations of independent and coupled MNPs are compared to experimental results. It is shown that the observed features are a natural consequence of the formation of chains and columns of MNPs during hyperthermia experiments: in these structures, when the MNP magnetocristalline anisotropy is small enough to be dominated by magnetic interactions, the hysteresis loop shape tends to be rectangular, which enhances their efficiency. On the contrary, when MNPs do not form chains and columns, magnetic interactions reduce the hysteresis loop squareness and the efficiency of MNPs compared to independent ones. Our finding can thus explain contradictory results in the literature on the influence of magnetic interactions on magnetic hyperthermia. It also provides an alternate explanation to some experiments where an enhanced specific absorption rate for MNPs in liquids has been found compared to the one of MNPs in gels, usually interpreted with some contribution of the brownian motion. The present work should improve the understanding and interpretation of magnetic hyperthermia experiments.

Magnetostrictive behaviors under rotating magneticfields are investigated for bcc(001) single-crystal films of Fe100-x-Six(x = 0, 6, 10 at. %). The magnetostriction observation directions are along bcc[100] and bcc[110] of the films. The magnetostriction waveform varies greatly depending on the observation direction. For the observation along [100], the magnetostriction waveform of all the films is bathtub-like and the amplitude stays at almost constant even when the magneticfield is increased up to the anisotropyfield. On the other hand, the waveform along [110] is triangular and the amplitude increases with increasing magneticfield up to the anisotropyfield and then saturates. In addition, the waveform of Fe90Si10 film is distorted triangular when the applied magneticfields are less than its anisotropyfield. These magnetostrictive behaviors under rotating magneticfields are well explained by employing a proposed modified coherent rotation model where the anisotropyfield and the magnetization reversal field are determined by using measured magnetization curves. The results show that magnetocrystalline anisotropy plays important role on magnetostrictive behavior under rotating magneticfields.

We characterized the magnetocrystalline anisotropy of a novel intermetallic compound, SmFe7, by means of torque measurement. Single crystal of SmFe7 was grown by the self-flux method using Sm as a flux. From an analysis of the torque curves in the (001) and (100) planes using the least mean squares method, we found that the tetragonal anisotropy constants K1, K2 and

The transition of the magnetization of multilayers [CeH2(x Å)/Fe(16 Å)]×n, x=10, 16, 25, from planar to perpendicular orientation at low temperatures is explained on a microscopic basis by performing angle- and temperature-dependent measurements of x-ray magnetic circular dichroism at the 2p absorption edge of Fe and at the 2p and 3d absorption edges of Ce. The 3d orbital magnetic moment in the Fe sublayers is considerably enhanced with respect to bulk bcc Fe and distinctly larger parallel to the layer normal than perpendicular to it. The Ce 4f states in these structures are well localized. The 4f magnetic moment is oriented along the layer normal due to a strong single-ion anisotropy resulting from crystal-field effects. The spin-split 3d states of Fe induce magnetic order on the Ce 5d states via hybridization and spin-orbit coupling, even on ions more distant from the interface. By intra-atomic 5d-4f exchange coupling the 4f states become magnetically polarized, with increasing strength toward low temperature. Together with the 5d-mediated 4f-3d coupling and the crystal-field induced single-ion 4f anisotropy this leads to a perpendicular orientation of the Fe 3d moment at low temperature. Hence the Ce 4f states are the motor of the reorientation transition of the multilayer magnetization. The 4f-5d exchange interaction in the hydrided Ce sublayers affects dramatically the spectral shape of the dichroic Ce 5d spectra and, at low temperature, the ratio of the integrated signals at the L2 and L3 edges.

Magnetization reversal modes in a thin-film NiFeCuMo ferromagnet (FM) with periodically varying in-plane anisotropy are studied by the magneto-optical indicator film (MOIF) technique. The uni-directional anisotropy in FM regions exchange-coupled to a FeMn antiferromagnet (AFM) film in the form of square mesh stripes is alternated by the uniaxial anisotropy in the FM regions inside this mesh. It is shown that the boundaries formed along the edges of these stripes, which separate FM regions with different anisotropy, crucially influence the kinetics of domain-structure transformation in both types of FM regions. It is established that the lateral exchange anisotropy in the ferromagnet, which is determined by the stabilization of the spin distribution in the FM layer along the FM-(FM/AFM) interface, leads to the asymmetry of the magnetization reversal in FM regions bordered with an FM/AFM structure. Anisotropy of the mobility of 180-degree "charged" and "uncharged" domain walls situated, respectively, perpendicular and parallel to the unidirectional anisotropy axis is revealed. The difference observed between the mobilities of charged and uncharged domain walls is attributed to the difference in the spin distribution in these walls with respect to the unidirectional anisotropy axis and is a key factor for the difference between the magnetization reversal kinetics in horizontal and vertical exchange-biased FM stripes. Drastic differences are revealed in the asymmetry of magnetization reversal processes in mutually perpendicular narrow stripes of FM/AFM structures. Possible mechanisms of magnetization reversal in low-dimensional FM-(FM/AFM) heterostructures are discussed with regard to the effect of domain walls localized on the edges of AFM layers.

A theory is proposed to account for the frequency dependence of the low field absorption of microwave energy by magnetic garnet films containing a stripe domain structure. Considering only the uniaxial anisotropyfield Hu and the demagnetization energy a Schro¨dinger like equation for the r.f. magnetization has been developed. Unbound states, for ?\\/?Hu?1, develop a net moment across a domain

A theory is proposed to account for the frequency dependence of the low field absorption of microwave energy by magnetic garnet films containing a stripe domain structure. Considering only the uniaxial anisotropyfield Hu and the demagnetization energy a Schrödinger like equation for the r.f. magnetization has been developed. Unbound states, for omega\\/gammaHu>~1, develop a net moment across a domain

A novel magneto-optical method has been used to probe the internal magnetic energy surface in 150×150×15 nm3 square Ni80Fe14Mo5 (``supermalloy'') nanomagnets which were fabricated by electron beam lithography. A strong fourfold symmetric anisotropyfield of strength 365+\\/-20 Oe is found, which confirms a recent prediction of the appearance of a configurational anisotropy due to the small deviations of the magnetization

A novel magneto-optical method has been used to probe the internal magnetic energy surface in 150×150×15 nm3 square Ni80Fe14Mo5 (``supermalloy'') nanomagnets which were fabricated by electron beam lithography. A strong fourfold symmetric anisotropyfield of strength 365+/-20 Oe is found, which confirms a recent prediction of the appearance of a configurational anisotropy due to the small deviations of the magnetization from the uniform state.

Neutron diffraction experiments have been carried out to study the magnetocrystalline anisotropy of two (2b and 2d) Tm sublattices and four (4f, 6g, 12j, and 12k) Fe sublattices in ferrimagnetic compound Tm{sub 2}Fe{sub 17} (space group P6{sub 3}/mmc). We have determined the temperature dependence of the magnitude and orientation of magnetization for each of the thulium and iron sublattices in the range (10-300) K. A spontaneous rotation (at about 90 K) of the Tm and Fe sublattice magnetizations from the c-axis to the basal plane is accompanied by a drastic change in the magnetization magnitude, signifying a large magnetizationanisotropy. Both Tm sublattices exhibit an easy-axis type of the magnetocrystalline anisotropy. The Fe sublattices manifest both the uniaxial and planar anisotropy types. The sublattice formed by Fe atoms at the 4f position reveals the largest planar anisotropy constant. The Fe atoms at the 12j position show a uniaxial anisotropy. We find that the inelastic neutron scattering spectra measured below and above the spin-reorientation transition are remarkably different.

A study about the magneticanisotropy and magnetostriction in ribbons of composition Fe81Al19 and Fe70Al30 obtained by the melt spinning technique is presented. The hysteresis loops indicate that the easy magnetization direction lies in both cases on the plane of the ribbon. Torque magnetometry measurements show that the in-plane magneticanisotropy constant results 10100 J m-3 and 490 J m-3 for the Fe81Al19 and Fe70Al30 respectively. After a thermal treatment of 2 h at 473 K to remove the residual stresses, the in-plane magneticanisotropy constants falls down to 2500 J m-3 in the first composition and remains the same in the second one, while the easy direction remains the same. Measurements of the magnetostriction and the residual stresses of both ribbons allow us to explain the above mentioned results about the magneticanisotropy and to conclude that the residual stresses via magnetostriction are the main source of magneticanisotropy in the case of Fe81Al19 ribbon but they do not influence this property in the ribbon of composition Fe70Al30.

This section of the Windows to the Universe website provides information and images about Earth's magneticfield (the magnetosphere), including detailed information about the aurora borealis, magnets, and solar wind. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging website that includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

It is noted that, for most of the mechanisms for the strong electric fields that characterize the narrow regions in which there is acceleration and precipitation of ring current and/or plasma-sheet plasma, certain effects must be taken into account in simulations of auroral electric fields. The effects are those of auroral particle anisotropy, of mirror forces due to the inhomogeneous geomagnetic field, of auroral electron backscatter by the atmosphere, and of electron trapping by the combination of magnetic mirroring and electrostatic forces. What is more, the effects of the very strong perpendicular electric field must also be taken into account in a kinetic description of the Poisson equation in order to achieve a unified theory of the auroral electrostatic structure. Progress in these areas during the past few years is reviewed. It is shown that particle anisotropies and mirror forces can account for some basic electrostatic features of the quiet arc, while additional effects may be occurring in strong events in which the parallel potential drop is more than about 10 kV.

Ferromagnetic/ferroelectric heterostructures have recently attracted significantly interest due to their potential applications in multifunctional electronic devices. We have recently predicted a magnetoelectric effect at the Fe/BaTiO3 interface induced by ferroelectric polarization reversal [1]. In this report, calculations are being carried out on the magneticanisotropy of Fe/BaTiO3 films. Preliminary results show that the ferroelectric switching of the BaTiO3 has appreciable effect on the magneticanisotropy of magnetic Fe films. This should be of interest in multiferroic device applications. [1] Chun-gang Duan, S. S. Jaswal, E. Y. Tsymbal, Phys. Rev. Lett. 97, 047201 (2006).

Spin Transfer Torque (STT) is of great interest in data writing scheme for the Magneto-resistive Random Access Memory (MRAM) using Magnetic Tunnel Junction (MTJ). Scalability for high density memory requires ferromagnetic electrodes having the perpendicular magnetic easy axis. We investigated CoZr as the ferromagnetic electrode. It is observed that interfacial magneticanisotropy is preferred perpendicular to the plane with thickness dependence on the interfaces with Pt layer. The anisotropy energy (K(u)) with thickness dependence shows a change of magnetic-easy-axis direction from perpendicular to in-plane around 1.2 nm of CoZr. The interfacial anisotropy (K(i)) as the directly related parameters to switching and thermal stability, are estimated as 1.64 erg/cm2 from CoZr/Pt multilayered system. PMID:25958513

We investigate the step decoration growth and magnetic properties of Fe grown on a curved Pt(111) single crystal by means of low-energy electron diffraction, scanning tunneling microscopy, and the surface magneto-optical Kerr effect. We find that the step-induced magneticanisotropy enhances the Curie temperature of Fe ultrathin films. Fe grown on high-vicinal-angle surfaces has larger values of both the saturation magnetization Ms and coercivity Hc compared with the flat surface. Ms(?) increases quadratically with the vicinal angle ? . The atomic steps of the vicinal surface greatly affect the magnetic properties of ultrathin Fe films. Finally we find that the step-induced surface anisotropy Ks(?) is proportional to ?4 . The surface anisotropy of Fe on curved Pt(111) substrate is related to the numbers of atoms at the step edges and the polarization of proximal Pt atoms.

We have prepared spin valves exhibiting perpendicular magneticanisotropy [perpendicular spin valves (PSVs)] by sputtering. These PSVs associate a "free" (Co/Pt) multilayer with a "pinned" (Co/Pt)/FeMn multilayer separated by various spacer materials (Pt, Cu, Al2O3). We carried out a comprehensive study of the magnetic and magnetotransport properties of the biased multilayers and of the complete spin valves. When the number of repeats in the (Co/Pt) exchange-biased multilayer is larger than 3, the samples present 100% remnant magnetization in the perpendicular configuration. The major hysteresis cycles exhibit two well-separated loops associated with the free and the exchange-biased (Pt/Co) multilayers. When optimized, the exchange-bias field can be larger than the coercivity of the pinned layer. Metallic PSVs with Cu spacers exhibit giant magnetoresistance but the amplitude is only of the order of 1% due to significant current shunting. In contrast, perpendicularly magnetized tunnel junctions are very promising.

Nickel (Ni) based nanoparticles and nanochains were incorporated as fillers in polydimethylsiloxane (PDMS) elastomers and then these mixtures were thermally cured in the presence of a uniform magneticfield. In this way, macroscopically structured-anisotropic PDMS-Ni based magnetorheological composites were obtained with the formation of pseudo-chains-like structures (referred as needles) oriented in the direction of the applied magneticfield when curing. Nanoparticles were synthesized at room temperature, under air ambient atmosphere (open air, atmospheric pressure) and then calcined at 400 °C (in air atmosphere also). The size distribution was obtained by fitting Small Angle X-ray Scattering (SAXS) experiments with a polydisperse hard spheres model and a Schulz-Zimm distribution, obtaining a size distribution centered at (10.0 ± 0.6) nm with polydispersivity given by ? = (8.0 ± 0.2) nm. The SAXS, X-ray powder diffraction, and Transmission Electron Microscope (TEM) experiments are consistent with single crystal nanoparticles of spherical shape (average particle diameter obtained by TEM: (12 ± 1) nm). Nickel-based nanochains (average diameter: 360 nm; average length: 3 ?m, obtained by Scanning Electron Microscopy; aspect ratio = length/diameter  10) were obtained at 85 °C and ambient atmosphere (open air, atmospheric pressure). The magnetic properties of Ni-based nanoparticles and nanochains at room temperature are compared and discussed in terms of surface and size effects. Both Ni-based nanoparticles and nanochains were used as fillers for obtaining the PDMS structured magnetorheological composites, observing the presence of oriented needles. Magnetization curves, ferromagnetic resonance (FMR) spectra, and strain-stress curves of low filler's loading composites (2% w/w of fillers) were determined as functions of the relative orientation with respect to the needles. The results indicate that even at low loadings it is possible to obtain magnetorheological composites with anisotropic properties, with larger anisotropy when using nanochains. For instance, the magnetic remanence, the FMR field, and the elastic response to compression are higher when measured parallel to the needles (about 30% with nanochains as fillers). Analogously, the elastic response is also anisotropic, with larger anisotropy when using nanochains as fillers. Therefore, all experiments performed confirm the high potential of nickel nanochains to induce anisotropic effects in magnetorheological materials.

Nickel (Ni) based nanoparticles and nanochains were incorporated as fillers in polydimethylsiloxane (PDMS) elastomers and then these mixtures were thermally cured in the presence of a uniform magneticfield. In this way, macroscopically structured-anisotropic PDMS-Ni based magnetorheological composites were obtained with the formation of pseudo-chains-like structures (referred as needles) oriented in the direction of the applied magneticfield when curing. Nanoparticles were synthesized at room temperature, under air ambient atmosphere (open air, atmospheric pressure) and then calcined at 400?°C (in air atmosphere also). The size distribution was obtained by fitting Small Angle X-ray Scattering (SAXS) experiments with a polydisperse hard spheres model and a Schulz-Zimm distribution, obtaining a size distribution centered at (10.0?±?0.6) nm with polydispersivity given by ??=?(8.0?±?0.2) nm. The SAXS, X-ray powder diffraction, and Transmission Electron Microscope (TEM) experiments are consistent with single crystal nanoparticles of spherical shape (average particle diameter obtained by TEM: (12?±?1) nm). Nickel-based nanochains (average diameter: 360?nm; average length: 3??m, obtained by Scanning Electron Microscopy; aspect ratio?=?length/diameter ? 10) were obtained at 85?°C and ambient atmosphere (open air, atmospheric pressure). The magnetic properties of Ni-based nanoparticles and nanochains at room temperature are compared and discussed in terms of surface and size effects. Both Ni-based nanoparticles and nanochains were used as fillers for obtaining the PDMS structured magnetorheological composites, observing the presence of oriented needles. Magnetization curves, ferromagnetic resonance (FMR) spectra, and strain-stress curves of low filler's loading composites (2% w/w of fillers) were determined as functions of the relative orientation with respect to the needles. The results indicate that even at low loadings it is possible to obtain magnetorheological composites with anisotropic properties, with larger anisotropy when using nanochains. For instance, the magnetic remanence, the FMR field, and the elastic response to compression are higher when measured parallel to the needles (about 30% with nanochains as fillers). Analogously, the elastic response is also anisotropic, with larger anisotropy when using nanochains as fillers. Therefore, all experiments performed confirm the high potential of nickel nanochains to induce anisotropic effects in magnetorheological materials.

Nematic and isotropic aqueous suspensions of beidellite clay sheets have been submitted to magnetic and a. c. electric fields. The nematic suspensions have positive anisotropy of magnetic susceptibility and negative anisotropy of electric susceptibility because the clay sheets orient their normals parallel to the magneticfield but perpendicular to the electric field. Moreover, the isotropic phase shows a large electric-field-induced birefringence. By dissolving acrylamide monomers in the clay suspensions and photopolymerization, clay/polymer composite gels could be elaborated. Aligned and patterned composites could be produced by application of an electric field during polymerization.

The effect of quantum well states on the magneticanisotropy of Co films grown on vicinal Cu(001) substrates was studied by in situ magneto-optic Kerr effect in a temperature range of 5 K to 365 K. The uniaxial magnetic ...

The effect of pressure anisotropy and flow velocity on the Kelvin-Helmholtz (KH) instability of two magnetized anisotropic pressure plasmas flowing relative to each other is investigated using generalized polytrope laws. The anisotropic pressure with the generalized polytrope laws is considered with three-dimensional perturbations in the description of plasma using relevant magnetohydrodynamic (MHD) set of equations. The magneticfield is assumed in the x-direction and parallel to the direction of the flow of plasma streams. A complete polytrope model is given for the considered system in terms of pressure components, magneticfield, and density of the fluids to discuss the condition of KH instability, stability, and overstability. The problem is solved using the normal mode analysis and the general dispersion relation is obtained by applying the appropriate boundary conditions. The case of nonvanishing wavenumber transverse to the direction of the stream is obtained, which represents the stationery configuration without excitation of KH instability. The longitudinal mode of propagation is discussed with conditions of KH instability, stability, and overstability for collisionless (anisotropic) double-adiabatic Chew-Goldberger-Low (CGL) and collisional (isotropic) MHD media, depending on various values of polytrope indices. The effects of pressure anisotropy, different flow velocities, and magneticfield are also discussed on the growth rate of KH instability. We observe that the presence of flow velocity and pressure anisotropy of the plasmas has a destabilizing influence on the growth rate of the system. The growth rate is found larger for MHD set of equations in comparison to the CGL set of equations. The presence of magneticfield has a stabilizing role on the growth rate of the considered system.

involving the anisotropic magnetic susceptibility of both the CNT and polymer systems. The anisotropyEnhancement of thermal and electrical properties of carbon nanotube polymer composites by magnetic. The alignment of CNTs in magneticfields arises from the anisotropic magnetic susceptibility of nanotubes.7

The dependence of the structural anisotropy of Fe-Si-B-Nb-Cu alloy on the applied stress during annealing has been studied by transmission x-ray diffraction. After crystallizing under stress, the Fe-Si nanocrystals show anisotropy in the lattice spacing of the (620) planes. Their elongations are proportional to the applied stress and show a linear correlation with the magneticanisotropy energy, K{sub u}. These results indicate that K{sub u} originates from a magnetoelastic effect due to an elastic elongation of the Fe-Si phase constrained by the surrounding amorphous phase.

The effects of CoFe thickness, Pt thickness, and number of CoFe\\/Pt bilayers on the anisotropy and coercivity of [CoFe\\/Pt]×n multilayer films have been studied. These parameters are varied in an attempt to deposite [CoFe\\/Pt]×n multilayer films with well-defined small perpendicular magneticanisotropies. Best results were obtained in a [CoFe 3 A&ring;\\/Pt 10 A&ring;]×5 film with coercivity Hc=42 Oe, perpendicular anisotropy

Birefringence is an indicator of structural anisotropy of materials. We measured the birefringence of Pb(II)-doped silica hydrogels prepared under a high magneticfield of various strengths. Because the silica is diamagnetic, one does not expect the structural anisotropy induced by a magneticfield. In previous work [Mori A, Kaito T, Furukawa H 2008 Mater. Lett. 62 3459-3461], we prepared samples in cylindrical cells made of borosilicate glass and obtained a preliminary result indicating a negative birefringence for samples prepared at 5T with the direction of the magneticfield being the optic axis. We have measured the birefringence of Pn(II)-doped silica hydrogels prepared in square cross-sectional cells made of quartz and reverted the previous conclusion. Interestingly, the magnetic-influenced silica hydrogels measured have been classified into four classes: two positive birefringent ones, no birefringent one, and negative birefringent one. Proportionality between birefringence and the strength of magneti...

A detailed study of the angular dependence of the magnetization reversal in polycrystalline ferromagnetic (FM)/antiferromagnetic Co/IrMn bilayers with noncollinear FM and unidirectional anisotropies shows a peculiar asymmetric magnetic behavior. The anisotropy configuration is set via a field cooling (FC) procedure with the magneticfield misaligned with respect to the easy magnetization direction of the FM layer. Different magnetization reversal modes are observed for either positive or negative angles with respect to the FC direction. The angular dependence of both coercivity and exchange bias also clearly displays the broken symmetry of the induced noncollinearity. Our findings are reproduced with a modified Stoner-Wohlfarth model including the induced anisotropy configuration. Our results highlight the importance of the relative angle between anisotropies in exchange bias systems, opening a new path for the tailoring of their magnetic properties.

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm2 coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO2 dot arrays formed on a Si wafer. At first, arrays of the SiO2 dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO2 dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO2 dots are about 24, 43, and 17 nm, respectively. Then {Co(0.4 nm)/Pt(0.08 nm)}8 MLs with a 3 nm Pt buffer layer is deposited onto the SiO2 dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO2 substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner-Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array.

Magneticanisotropy (MA) energy induced by uniform lattice deformation is calculated for cobalt-ferrites Fe(Co-Fe)2O4 (CFOs) by using an electron theory for down-spin t2g electrons of Co2+ ions in CFOs. It is shown that the MA energy depends nonlinearly and asymmetrically on the uniform lattice deformation. By comparing the calculated results with those obtained in the phenomenological theory at the small lattice deformation limit, values of the magnetoelastic coefficients B1 and B2 have been evaluated. These values semi-quantitatively agree with the experimental ones. A non-trivial appearance of crystal-field potentials produced by the uniform trigonal lattice deformation is crucial to understand the large negative value of B2.

Experimental results for the properties of ultrasonic propagation velocity in kerosene-based and water-based magnetic fluids are reported. Ultrasonic wave frequencies of 1MHz, 2MHz and 4MHz are used and the measurement scheme is based on the pulse method. The external magneticfield intensity is varied from 0mT to 550mT and the angle between the magneticfield direction and the direction of ultrasonic wave propagation is varied from 0° to 90°. The ultrasonic propagation velocity in magnetic fluids is dependent on temperature, elapsed time of applying the magneticfield, and magneticfield intensity. Hysteresis and anisotropy of ultrasonic propagation velocity are observed. These interesting results seem to be related to chain-like cluster formation in the magnetic fluids and the characteristic period of Brownian motion of the magnetic particles.

A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.

The lightning magneticfield is simulated when a pulse current is injected into the loop from the lightning surge generator. Different waveforms of lightning magneticfield can be simulated by regulating the parameters of the loop according to the relation between the parameters of the loop and the simulated wave. The dot loop is made to measure the magneticfield

The magneticfield experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magneticfield throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the MagneticField Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and

In many applications of magnetic resonance imaging large linewidths means that to achieve useful resolution in the image large magneticfield gradients should be employed. This paper outlines the principles of stray field imaging that utilises the large gradients intrinsic to the fringe field of superconducting solenoidal magnets. Examples of images from strongly broadened everyday objects are given.

Formation and existence of magnetic skyrmion-like configurations in bilayer nanodisks {Ta(3 nm)/[Co(0.37 nm)/Ni(0.58 nm)]10}2 with perpendicular magneticanisotropy are shown experimentally at room temperature. Magnetization reversal through the skyrmion state is studied using magnetic hysteresis measurements. An evolution of skyrmion configurations in the nanodisk structure is analyzed. Experimental methods and micromagnetic simulations help to understand the magnetization reversal processes occurring through the stable skyrmion-like configurations. Formation of the intermediate C-states during magnetization reversal is demonstrated. The skyrmion number for all possible spin configurations is calculated.

We study a homogeneous and nearly-isotropic Universe permeated by a homogeneous magneticfield. Together with an isotropic fluid, the homogeneous magneticfield, which is the primary source of anisotropy, leads to a plane-symmetric Bianchi I model of the Universe. However, when free-streaming relativistic particles are present, they generate an anisotropic pressure which counteracts the one from the magneticfield such that the Universe becomes isotropized. We show that due to this effect, the CMB temperature anisotropy from a homogeneous magneticfield is significantly suppressed if the neutrino masses are smaller than 0.3 eV.

In this paper, we investigate the magnetic properties of Fe50 Co50 polycrystalline thin ?lms, grown by dc-magnetron sputtering, with thickness (t) ranging from 2.5 nm up to 100 nm. We focused on the magnetic properties of the samples to highlight the effects of possible intrinsic stress that may develop during growth, and their dependence on ?lm thickness. Indeed, during ?lm deposition, due to the growth technique and growth conditions, a metallic ?lm may display an intrinsic compressive or tensile stress. In our case, due to the Fe50Co50 magnetolastic properties, this stress may in its turn promote the development of magneticanisotropies. Samples magnetic properties were monitored with a SQUID magnetometer and a magneto-optic Kerr effect apparatus, using both an in-plane and an out-of-plane magnetic ?eld. Magnetoresistance measurements were collected, as well, to further investigate the magnetic behavior of the samples. Indications about the presence of intrinsic stress were obtained accessing samples curvature with an optical pro?lometer. For t ? 20 nm, the shape of the in-plane magnetization loops is squared and coercivity increases with t, possibly due to fact that, for small t values, the grain size grows with t. The magnetoresistive response is anisotropic in character. For t > 20 nm, coercivity smoothly decreases, the approach to saturation gets slower and the shape of the whole loop gets less and less squared. The magnetoresistive effect becomes almost isotropic and its intensity increases of about one order of magnitude. These results suggest that the magnetization reorientation process changes for t > 20 nm, and are in agreement with the progressive development of an out-of-plane easy axis. This hypothesis is substantiated by pro?lometric analysis that reveals the presence of an in-plane compressive stress.

We studied Co/Cu/Co pseudo-spin-vales (PSVs) for induced anisotropy during film growth and its effects on the magnetization and magnetoresistance (MR). Considerable improvement of MR performance was achieved in these PSVs with Fe buffer due to anisotropy induced in <100> direction compared to PSVs on Cr/Cu buffer. PSVs were deposited on Si (100) wafers with natural oxide using S-research magnetron sputtering in 3 mTorr argon and base pressure <1.0x10-7 Torr. The PSVs with different thickness values of the constituent layers were deposited to optimize their MR performance. For PVS on Fe buffer, sharp magnetization reversal results in an almost perfect ``square loop" of magnetization and a corresponding enhanced MR value (9.2%) and field sensitivity (1.0%Oe)at the switch field of 27 Oe. The dependence of the magnitude of the MR on the thickness of constituent layers of the PSVs was interpreted within the model based on first principles solution to the Boltzmann transport equations calculations. The magnetization reversal of the PSVs with Cr/Cu buffer was affected by the temperature, unlike the anisotropic PSVs with the Fe buffer layer, which showed perfect square loops and high MR sensitivity from 5 K to 300 K. In both systems the switching field between low and high resistance states decreased with increasing temperature but it is lower for the Fe/Co/Cu/Co.

We adopted a novel method to tune the terrace width of Si(111) substrate by varying the direction of heating current. It was observed that the uniaxial magneticanisotropy (UMA) of Fe films grown on the Si(111) substrate enhanced with decreasing the terrace width and superimposed on the weak six-fold magnetocrystalline anisotropy. Furthermore, on the basis of the scanning tunneling microscopy (STM) images, self-correlation function calculations confirmed that the UMA was attributed mainly from the long-range dipolar interaction between the spins on the surface. Our work opens a new avenue to manipulate the magneticanisotropy of magnetic structures on the stepped substrate by the decoration of its atomic steps. PMID:23529097

We adopted a novel method to tune the terrace width of Si(111) substrate by varying the direction of heating current. It was observed that the uniaxial magneticanisotropy (UMA) of Fe films grown on the Si(111) substrate enhanced with decreasing the terrace width and superimposed on the weak six-fold magnetocrystalline anisotropy. Furthermore, on the basis of the scanning tunneling microscopy (STM) images, self-correlation function calculations confirmed that the UMA was attributed mainly from the long-range dipolar interaction between the spins on the surface. Our work opens a new avenue to manipulate the magneticanisotropy of magnetic structures on the stepped substrate by the decoration of its atomic steps. PMID:23529097

Amorphous silicate is considered to be one of the major dust-forming material, however its possibility of magnetic alignment by magneticanisotropy has not been considered as yet. This is because the anisotropy of an amorphous material is generally considered to be negligibly small. In the present study, depth profile of paramagnetic anisotropy ??para was experimentally obtained for the first time on an amorphous silicate sample, namely moldavite, with a spatial resolution of 0.5 mm. For the above purpose, ??para of square plate (2 mm×2 mm×0.5 mm), separated from a quadrangular prism (2 mm×2 mm×10 mm), were measured one by one; the prism was cut from the amorphous sample with its long axis directed normal to the surface. In order to realize the above measurement, a new experimental device was adopted which could detect ??para of a sub-mm sized sample by measuring its field-induced rotational oscillation in an ?G area. The observed magnetic unstable axis of the plate was always normal to surface plane. The magnitude of ??para at the surface was at a level of 10-6 emu/g, which was comparable to the value previously obtained for of olivine and pyroxene, which are major dust components in the proto-planetary disk region. Accordingly, most of the dust forming materials in the above region is expected to possess finite amount of ?? to cause partial dust alignment.

An experimental investigation using magnetooptical magnetometry is described into the dependence of susceptibility and hysteresis on the lateral size (30-500 nm), thickness (3-7.5 nm), and geometric shape (triangular, square, and pentagonal) of supermalloy nanomagnets made by electron beam lithography. We show that as the lateral size of the nanomagnets is reduced, magnetic softness is at first reduced and then increases abruptly. We show that this increase in softness is due to thermal fluctuations overcoming the anisotropy imposed by the geometric shape of the nanomagnets, leading to superparamagnetism. Nanometer scale magnetic elements with high susceptibility, zero hysteresis, and saturation fields of a few oersteds can thus be made. Implications for field sensing technology are discussed.

The 3 d transition-metal oxides (TMOs) are subject of debate since many decades due to their extraordinary properties, such as the formation of an antiferromagnetic ordering AFM2 below their Néel temperature. Many studies, both experimental and theoretical, focus only on MnO and NiO, where the crystalline anisotropy is solely driven by exchange striction along the unique symmetry axis in the [111] direction and where the magneticanisotropy is explained in terms of magnetic dipole interactions. In the other TMOs, FeO and CoO, however, orbital magnetization and spin-orbit interaction play an additional, yet crucial role for both crystalline and magneticanisotropy. We present density-functional theory (DFT) studies including an on-site interaction U of the crystalline and magneticanisotropy of the electronic systems with non-collinear spins. The influence of the (semi-)local description of exchange and correlation (XC) by means of the local density approximation (LDA) and generalized gradient approximation (GGA) on the orbital moments in FeO and CoO and the implications on the aforementioned properties is investigated. We discuss the quenching of the orbital magnetization due to the gradient corrections.

Soft ferromagnetic dots with sub-micrometer size can exhibit in the ground state a curling spin configuration known as magnetic vortex. In the case of soft ferromagnetic materials in micron and submicron scales, small changes in shape, size and material's anisotropy can modify the energy equilibrium that defines the stable spin structure. In this work, we investigated the magnetic configuration of micron-sized Co60Fe40 and Permalloy disks and elipses, prepared by lift-off lithography process, by comparing the results of micromagnetic simulations and magnetic force microscopy (MFM) measurements. By comparing the results for Co60Fe40 and Permalloy it is possible to elucidate the effect of the planar magnetocrystaline anisotropy in the stability of the magnetic vortex configuration and this effect is compared with the effect of the shape anisotropy induced by the elliptical shape. The results for disks with diameters between 0.5 and 8 ?m showed that the anisotropy favors spins alignment and domains division, reducing vortex stability. The results showed different magnetic configurations for each disk diameter. Additionally, a statistical analysis of the magnetic configuration distribution observed in MFM experiments was performed and compared with the simulation results. Acknowledgements: CAPES, CNPq and FAPEMIG.

Spintronic materials with strong perpendicular magneticanisotropy (PMA), such as Co/Pd, Co/Pt and Co/Ni multilayers, have been introduced to improve the functional performance of STT devices (e.g. enhanced thermal stability, scalability and switching speeds of spin memory/logic). Furthermore, by coupling magnetic layers with PMA and longitudinal magneticanisotropy (LMA), added benefits such as a variable magnetization tilt angle and tunable damping have been shown. In our study, we discuss how to precise control the anisotropy tilt angle by coupling the PMA hard layer (Co/Pt) with an in-plane soft layer (IMA, CoFeB). Due to the competition between the PMA and IMA, the tilted angle can be tuned by varying thickness of IMA. The stack of Pt(5nm)/Co (1nm)/CoFeB(Xnm)/MgO (2nm) (x varied from 0 to 1nm) was deposited by magneto-sputtering system. The magnetic properties were investigated by vibrating sample magnetometer and anomalous Hall effect . The electric transport of microscale devices comprised of that stack were also studied by our probe station with electromagnet. The experiments show the magneticanisotropy can be tuned well by changing thickness of in plane layer and open a promising new avenue to next generation spintronics devices.

The magnetic studies were performed on sites of reddish-brown sandstones, siltites, and mudstones, which crop out mainly in Mato Grosso do Sul State. Magnetic fabrics were determined on oriented cylindrical specimens (2.54 cm x 2.2 cm) using anisotropy of low-fieldmagnetic susceptibility (AMS). Considering the eingenvector orientations, the sites usually gave good results. The analysis at the individual-site scale defines two AMS fabric types. The first type shows Kmin perpendicular to the bedding plane, while Kmax and Kint are scattered within the bedding plane itself. This fabric is usually interpreted as primary (sedimentary-compactional), typical of undeformed sediments and is dominant among the sites. The second type shows good clustering of the AMS principal axes with Kmin still either perpendicular or sub-perpendicular to the bedding plane. This fabric type could be interpreted as a combination of sedimentary-compactional and tectonic contributions if some strain markers or evidence for tectonic deformation had been found in the studied area. However, the tight Kmax grouping in this fabric type could be explained by the action of currents since they cause Kmax to be aligned sub-parallel to the paleocurrent direction.

Using the Oseen-Zöcher-Frank theory, in the steady state, I study the distortion energy of a disclination line in nematic liquid crystal in the presence of an external magneticfield. The director field around a disclination line is exactly calculated by minimizing the total free energy. The behavior of total free energy as a function of magneticfield for two kinds of nematic material (positive and negative magneticanisotropy) are discussed. In the short distance limit, the total free energy per unit length is calculated. In this case, the magnetic dependence of total free energy is discussed.

The magnetic properties of tetragonal YFexMn12-x compounds, which crystallize in the ThMn12 -type structure, are governed by both strong competing exchange interactions between the magnetic moments on three nonequivalent sites 8i , 8j , and 8f occupied by Mn (Fe) atoms preferentially in 8i (8f) and Mn-planar (Fe-axial) magnetocrystalline anisotropies. Using low field ac magnetic susceptibility versus temperature, zero-field-cooled and field-cooled magnetization versus temperature, and applied magneticfield, specific heat, x-ray-absorption spectroscopy at FeK and MnK edges, and neutron-diffraction experiments, the magnetic phase diagram of YFexMn12-x has been determined. Up to six different phases were found as a function of the Fe concentration x . Some of them have not been thoroughly investigated until now. In particular, the antiferromagnetic ordering of the itinerant YMn12 is different from the phase proposed before, and the spin-glass-like phase observed at low temperatures for 2?x?6 has been characterized in more detail. Contrary to other intermetallic Mn-based systems, the magnetism in YFexMn12-x cannot be correlated in a straightforward way to 3d-3d distances and it seems to be more sensitive to the electronic density and the localization-delocalization of electronic band states on the three sites 8i , 8j , and 8f .

When charged particles move in a random magneticfield superposed upon a relatively large constant field, their pitch-angle distribution can be calculated to any desired precision by an iterative approximation procedure. Improved knowledge of the pitch-angle distribution and of the characteristic time for relaxation of anisotropy leads to an accurate expression for the coefficient of diffusion parallel to the mean field.

We present broadband ferromagnetic resonance measurements of tunable spin wave anisotropy in arrays of nanodots with different dot shapes. Magnetization dynamics of the circular dot array shows two modes, while square, diamond, and triangular dot arrays show three, three, and four modes, respectively. Various distinct rotational symmetries in the configurational anisotropy of the nanodot arrays are observed with the variation of dot shape. The observed spin wave modes are reproduced by micromagnetic simulations and the calculated mode profiles show different collective modes determined by internal and stray magneticfields. Effects of dot shapes are observed in combination with the effects of lattice symmetry and the shape of the boundary of the array. The collective behaviour is observed to be weakest in the diamond shaped dots and strongest in circular shaped dots. This is further confirmed by the stray field calculation. The large variation of spin wave mode frequencies and their configurational anisotropies with dot shapes are important for selection of suitable basis structures for future magnonic crystals.

The authors introduce a new parameter, the shear angle of vector magneticfields, ??, to describe the non-potentiality of magneticfields in active regions, which is defined as the angle between the observed vector magneticfield and its corresponding current-free field. In the case of highly inclined field configurations, this angle is approximately equal to the "angular shear", ??, defined by Hagyard et al. (1984). ?? can be considered as the projection of the shear angle, ??, on the photosphere. For the active region studied, the shear angle, ??, seems to have a better and neater correspondence with flare activity than does ??. It gives a clearer explanation of the non-potentiality of magneticfields. It is a better measure of the deviation of the observed magneticfield from a potential field, and is directly related to the magnetic free energy stored in non-potential fields.

A STUDY OF MAGNETICANISOTROPY ENERGY IN CuMn SPIN GLASS A Thesis by CHRISTINE ADELE ALLEN Submitted to the Graduate College of Texas ARM University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE August 1986... Major Subject: Physics A STUDY OF MAGNETICANISOTROPY ENERGY IN CuMn SPIN GLASS A Thesis by CHRISTINE ADELE ALLEN Approved as to style and content by: Thomas W. Adair, III (Chai man of Committee) Robert A. enefick (Member) Donald L. Parker...

FePt/AlN layered structures were deposited onto fused quartz substrate by magnetron sputtering method and found to show in-plane anisotropy. However, annealing of the films leads to a transition of magneticanisotropy from in-plane to perpendicular direction, and the perpendicular anisotropy gets stronger as the annealing temperature increases. Structural analysis shows that the FePt and AlN layers are textured with (111) and (002) orientations, respectively, along the film normal, and no ordering transformation is found for FePt alloy. To study the origin of the developed anisotropy, stress condition was analyzed with an equal biaxial stress model using X-ray diffraction 2 ?- ? scan method and interface quality was evaluated by X-ray reflectivity measurement and transmission electron microscopy observation. The results reveal that perpendicular magneticanisotropy of the annealed FePt/AlN layered structure can be attributed to the enhanced interface anisotropy, which is due to flattening of the interfaces through annealing.

Compositional dependence of saturation magnetization, magnetostriction and creep-induced magneticanisotropy is investigated in amorphous (Fe1-xCox)85B15 alloys. A close correlation of the three quantities was found. An anomaly centred at x=0.25 may indicate chemical short-range order of the Fe3Co type in this concentration range. An explanation of the creep-induced anisotropy behaviour based on the bond-orientational anisotropy model is presented. It takes

Diffusion weighted imaging uses the signal loss associated with the random thermal motion of water molecules in the presence of magneticfield gradients to derive a number of parameters that reflect the translational mobility of the water molecules in tissues. With a suitable experimental set-up, it is possible to calculate all the elements of the local diffusion tensor (DT) and derived parameters describing the behavior of the water molecules in each voxel. One of the emerging applications of the information obtained is an interpretation of the diffusion anisotropy in terms of the architecture of the underlying tissue. These interpretations can only be made provided the experimental data which are sufficiently accurate. However, the DT results are susceptible to two systematic error sources: On one hand, the presence of signal noise can lead to artificial divergence of the diffusivities. In contrast, the use of a simplified model for the interaction of the protons with the diffusion weighting and imaging field gradients (b matrix calculation), common in the clinical setting, also leads to deviation in the derived diffusion characteristics. In this paper, we study the importance of these two sources of error on the basis of experimental data obtained on a clinical magnetic resonance imaging system for an isotropic phantom using a state of the art single-shot echo planar imaging sequence. Our results show that optimal diffusion imaging require combining a correct calculation of the b-matrix and a sufficiently large signal to noise ratio. PMID:24761372

We present a new approach for modeling magnetic hysteresis curves of ultrathin magnetic films and multilayers. The model is based on a free -energy minimization approach in which spin reorientation kinetics are treated via coherent rotation with the additional provision that the magnetization can jump between local minima. This introduces the possibility of a novel latched state when the magnetization

The effects of CoFe thickness, Pt thickness, and number of CoFe /Pt bilayers on the anisotropy and coercivity of [CoFe/Pt]×n multilayer films have been studied. These parameters are varied in an attempt to deposite [CoFe/Pt]×n multilayer films with well-defined small perpendicular magneticanisotropies. Best results were obtained in a [CoFe3Å/Pt10Å]×5 film with coercivity Hc =42Oe, perpendicular anisotropy Hk=2200Oe, and easy-axis remanence Mr /Ms=1. Large Pt thickness tends to cause well-defined interfaces thus larger surface anisotropy. Large CoFe thickness and more number of bilayers tend to cause bow-tie shaped easy-axis loops and multiple domain structures.

The superconductor TmNi2B2C possesses a significant fourfold basal plane anisotropy, leading to a square vortex lattice (VL) at intermediate fields. However, unlike other members of the borocarbide superconductors, the anisotropy in TmNi2B2C appears to decrease with increasing field, evident by a reentrance of the square VL phase. We have used small-angle neutron scattering measurements of the VL to study the field dependence of the anisotropy. Our results provide a direct, quantitative measurement of the decreasing anisotropy. We attribute this reduction of the basal plane anisotropy to the strong Pauli paramagnetic effects observed in TmNi2B2C and the resulting expansion of vortex cores near Hc2.

Torsion pendulum magnetometer measurements on ferrites and on neodymium-iron-boron permanent magnets are presented. The damping of the oscillation of the pendulum leads to information on the magnetic energy losses of the magnets in a small alternating magneticfield applied perpendicular to a bias field. The origin of the energy absorption is explained by the magnetization reversal of single-domain particles. It is shown experimentally that the energy absorption mechanism requires the ferromagnetic order of the sample, and that the magneticfield strength of maximal energy absorption coincides with the effective anisotropyfield strength.

We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magneticfield. The torque is calculated using the Barash theory of dispersive torques. In III-IV semiconductors such as InSb, the effect of an external magneticfield is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magneticfield parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of InSb. In the absence of magneticfield there is no torque. As the magneticfield increases, the optical anisotropy of InSb increases and the torque becomes different from zero, increasing with the magneticfield. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropic materials when the magneticfields is close to 1 T.

We investigated the dependencies of both the magnetization characteristics and the perpendicular magneticanisotropy of CoxFe3-xO4(001) epitaxial films (x = 0.5 and 0.75) on the growth conditions of the reactive magnetron sputtering process. Both saturation magnetization and the magnetic uniaxial anisotropy constant Ku are strongly dependent on the reactive gas (O2) flow rate, although there is little difference in the surface structures for all samples observed by reflection high-energy electron diffraction. In addition, certain dead-layer-like regions were observed in the initial stage of the film growth for all films. Our results suggest that the magnetic properties of CoxFe3-xO4 epitaxial films are governed by the oxidation state and the film structure at the vicinity of the interface.

This study enlightens how the magneticanisotropy might be tailored in magnetic films by the proper choice of the substrate. Single crystalline (111)SmAl{sub 2} films have been grown by molecular beam epitaxy on two substrates: (1120)Al{sub 2}O{sub 3} and (111)CaF{sub 2}. Hysteresis loops measured along the different crystallographic directions are the signature of the following: (i) a uniaxial anisotropy with an easy direction perpendicular to the (111) growth plane when the film is grown on Al{sub 2}O{sub 3}; (ii) a [111] hard magnetic direction when the film is grown on CaF{sub 2}. This effect can be understood if we consider the influence of the thermal strains on the various energy terms which govern the easy magnetization direction. The relevant parameters to determine the easy magnetization direction are the relative sign and absolute values of the strains and of the magnetoelastic constants.

The magnetic properties of CoFeB thin films grown on flexible polyimide substrates were investigated using a magneto-optical Kerr effect magnetometer. In-plane uniaxial magneticanisotropy was observed in the virgin state. The strain induced by bending the flexible substrate was applied on the sample to change the magnetic properties of CoFeB. The strain induced uniaxial magneticanisotropy changed linearly with the deformation by about 8.41 × 1041 erg/cm3 at 1% of deformation. Our results prove the magnetic properties of CoFeB grown on flexible polyimide substrate can be tuned effectively by bending, which could be important for future flexible spintronics. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB922201 and 2015CB921401) and the National Natural Science Foundation of China (Grant Nos. 11174272, 11474272, 11274371, 51431009, and 61225021).

Amorphous CoSiB/Pt multilayer is a perpendicular magneticanisotropy material to achieve high squareness, low coercivity, strong anisotropy, and smooth domain wall (DW) motion, because of the smoother interface compared with crystalline multilayers. For [CoSiB(6 Å)/Pt (14 Å)]N multilayers with N = 3, 6, and 9, we studied the field-induced DW dynamics. The effective anisotropy constant K1eff is 1.5 × 106 erg/cm3 for all the N values, and the linear increment of coercive field Hc with N gives constant exchange coupling J. By analyzing the field dependence of DW images at room temperature, a clear creep motion with the exponent ? = 1/4 could be observed. Even though the pinning field Hdep slightly increases with N, the pinning potential energy Uc is constant (=35 kBT) for all the N values. These results imply that the amorphous [CoSiB/Pt]N multilayers are inherently homogeneous compared to crystalline multilayers. For N ? 6, the pinning site density ?pin is less than 1000/?m2, which is about 1 pinning site per the typical device junction size of 30 × 30 nm2. Also, the exchange stiffness constant Aex is obtained to be 0.48 × 10-6 erg/cm, and the domain wall width is expected to be smaller than 5.5 nm. These results may be applicable for spin-transfer-torque magnetic random access memory and DW logic device applications.

The modulation of the magneticanisotropy using the electronic features of the ligands was monitored by performing magnetic, spectroscopic and theoretical studies on a series of {Fe2Dy2} coordination clusters. PMID:24022666

Magnetic CoxC nanorods with larger magnetocrystalline anisotropy of 5×105 J/m3 as well as larger coercivity and lower Curie temperature are introduced. The particles have an average diameter of 8 nm and shows three different magnetic behaviors. The sample shows ferromagnetism up to 400 K, superparamagnetism at temperature >400 K and magnets, magnetic sensors and contract agent for magnetic resonance imaging.

Model calculations and magnetic resonance experiments were employed to investigate the microscopic and macroscopic properties of amorphous neodymium-iron and neodymium-cobalt thin films. The calculations yielding the magnetization as a function of the applied field and temperature, the coercivity, and the ordering temperature, were performed on a random dense packed model of an amorphous neodymium -iron thin film. The model includes

We have studied the effects of uniform external magneticfields on driven magnetohydrodynamic (MHD) turbulence, including, as a limit, the case of zero external field. We have two main results. First, as the strength of the external field is increased, the kinetic energy density drops by roughly the product of the rms velocity (V) and the strength of the external field (B0). The magnetic energy density rises by roughly the same amount. Consequently, the rms magneticfield is always much greater than the external field. Second, when the external magneticfield (in velocity unit) is not very strong (say, less than 0.1 times the rms velocity) the induced magneticfield remains almost isotropic, i.e. there is no apparent anisotropy of order B0/V. We discuss implications of these results on some recent work on mean-field dynamo theories. To explain the dependence of the kinetic and magnetic energy densities on the mean field external field, we present a simple model based on the assumption of fast turbulent diffusion processes. We have also confirmed our previous result that the magneticfields are amplified through field line stretching at a rate proportional to the difference between the velocity and the magneticfield strength times a constant. This work was partially supported by National Computational Science Alliance under CTS980010N and utilized the NCSA SGI/CRAY Origin2000.

This research is focused on the development of pulse electrodeposition techniques to fabricate a high-density array of vertically oriented, high-magneticanisotropy cobalt nanowires using a porous polymer film template. This type of array is a competitive candidate for future perpendicular magnetic media capable of storage densities exceeding 1 Terabit/in.{sup 2} The polymer template, derived from a self-assembling P(S-b-MMA) diblock copolymer film, provides precise control over the nanowire diameter (15 nm) and interwire spacing (24 nm), whereas nanowire length (typically 50 to 1000 nm) is controlled accurately with the aid of real-time electrochemical quartz crystal monitoring. Pulse and pulse-reversed electrodeposition techniques, as compared to dc, are shown to significantly enhance the perpendicular magneticanisotropy of the magnetic nanowire array and ultimately result in coercivity as large as 2.7 kOe at 300 K. Magnetic and structural characterizations suggest that these properties arise from an improved degree of magnetocrystalline anisotropy (due to c-axis oriented crystal growth and improvements in crystal quality) that strongly supplements the basic shape anisotropy of the nanowires. Low temperature magnetometry is used to investigate exchange bias effects due to the incorporation of CoO antiferromagnetic impurities during the electrodeposition process and subsequent Co oxidation in air.

(version 6/26/06) MagneticFields GOALS (1) To visualize the magneticfields produced by several to trace out the magneticfield lines of a single bar magnet on a large sheet of paper. (3) To calculate where the magneticfields of the Earth and the bar magnet sum to zero. INTRODUCTION A magneticfield

We show that the ferromagnetic anisotropy of a thin crystalline Fe3O4 film can be manipulated in situ via the application of tunable stress. The stress is exerted by a piezoelectric actuator, onto which the Fe3O4 film is cemented. The strain in the sample is quantified as a function of the voltage applied to the actuator using high-resolution x-ray diffraction, and

Expressions describing the energy loss of a charged particle in a Maxwellian plasma with a strong magneticfield are described. The dielectric constant found by means of quantum-mechanical correlation functions is used. The Coulomb logarithm is calculated for strong magneticfields and is found to be a function of the magneticfield. The anisotropy of the energy loss of a slow test particle in terms of the direction of the particle's velocity with respect to the magneticfield is described. Calculations are carried out for the slow test particles. It is concluded that the rate of energy loss of a slow test particle as it moves across a strong magneticfield is some 1.2-1.5 times the energy loss rate for a particle moving along the magneticfield. It is also shown that the anisotropy grows with increasing magneticfield.

The alloy of TbFe2 was studied by ball milling with and without the presence of external magneticfield. While the structure and powder morphology of the alloy were investigated using scanning electron microscope and X-ray diffraction, the magnetization was investigated using vibrating sample and superconducting quantum interference device magnetometers. The rate of particle reduction with ball milling is comparatively higher in the presence of external magneticfield than without it. Consequently, owing to a large fraction of particles acquiring near single domain configuration under the field assisted milling condition, the coercivity derived from these particles are as high as 6500 Oe than that of particles obtained without the aid of external magneticfield which is around 3850 Oe. The field cooled low temperature magnetization exhibits a large coercivity and skew in the shape of the magnetization curve due to the large anisotropy.

The Beaver River Diabase (BRD) is a series of mafic dikes and sills within the Beaver Bay Complex (BBC) of northern Minnesota, which formed during the development of the ~1.1 Ga Midcontinent Rift (MCR). The BRD is one of the youngest and most extensive intrusive phases of the BBC. The BRD dikes and sills were emplaced into the medial levels of the 6-10 kilometer-thick North Shore Volcanic Group and occur over an arcuate area extending 120 by 20 kilometers. The BRD is composed of fine- to medium-grained ophitic olivine gabbro and does not display obvious foliation or lineation features and rarely displays modal layering. Without obvious magmatic internal structures, it is difficult to determine emplacement properties such as flow direction using standard geologic mapping or petrographic techniques. For this reason, we measured the anisotropy of magnetic susceptibility (AMS), in conjunction with other rock magnetic properties, to better understand the BRD's emplacement and deformation history in the context of the MCR. AMS measures the directional dependence of low-fieldmagnetic susceptibility, and is used to infer a shape-preferred orientation of magnetic minerals within a rock, which can be related to specific emplacement mechanisms (e.g. directional flow or settling). Preliminary analysis of AMS at 20 sites within the southern half of the BRD (with 4-7 samples per site) shows maximum susceptibility values between 4.48 x 10-6 and 2.22 x 10-4 m 3/kg (1165 and 65400 ?SI). Most specimens display nearly isotropic AMS ellipsoids (Pj < 1.15) with minor degrees of prolateness and oblateness. However, about 20% of specimens have higher anisotropies (Pj between 1.15 and 1.67) and higher degrees of oblateness and prolateness. Variations in AMS properties may reflect differences in concentration and composition of magnetic minerals, as well as emplacement mechanisms. Measurements of susceptibility as a function of temperature yield Curie points between 470 and 570 °C, indicating the presence of low-titanium titanomagnetite. Major hysteresis loops show coercivities between 1 and 25 mT, consistent with titanomagnetite as the dominant remanence carrier.

The investigation of a pentagonal bipyramidal Co(ii) complex with large positive anisotropy (D ? +30 cm(-1)) revealed field induced Single-Molecule Magnet behaviour with Ueff ? 50 K at 1.0 kOe. This compound belongs to a group of only a handful of complexes which exhibit this unique magnetic property while possessing easy-plane anisotropy. At high applied fields, a second relaxation process with an intermolecular nature has been exposed using magnetic dilution studies with varying percentages of Zn(ii) analogue. The disappearance of the second relaxation process at low frequency can be followed using magnetically diluted samples at 25%, 10% and 5% Co(ii) concentrations. PMID:25742046

A new method, anisotropy of complex magnetic susceptibility (ACMS), for determining the petrofabric of specimens with conductive minerals is developed. The method uses the same induction coil equipment and techniques that can be used for the measurement of the anisotropy of magnetic susceptibility (AMS). However, a higher (100 kHz) operating frequency emphasizes the electrical conductivity response and thus yields a measure of the anisotropy of electrical conductivity of the specimen. The method was tested on variably deformed plasticine samples containing aluminium fabric markers and on synthetic aggregates of pyrrhotite and talc-pyrrhotite mixtures deformed triaxially at a confining pressure of 200 MPa (2 kbar) by up to 35% homogeneous shortening. ACMS successfully defines the petrofabric and permits prediction of the principal directions of finite strain. The intensity of AMS and, to a lesser extent, of ACMS correlate with the strain ratio in these simple, coaxial, flattening plane strain experimental deformations on selected materials.

Calculations were made to predict magneticfield intensities surrounding an aircraft following a lightning strike. Aircraft design and aircraft structural geometry were considered in the computations. A wire grid aircraft model was used to aid in magnetic flux estimation.

The magneticfields of degenerate stars are discussed with emphasis on such basic issues as how their magneticfield strengths are determined, their origin, and evolution. The magneticfields of both white dwarfs and neutron stars are discussed together, and it is speculated that the origin and evolution of their fields may be related. It is also suggested that it may be possible to apply and test models for the evolution of the magneticfields in neutron stars by using white dwarfs and vice versa.

The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magneticfield which is produced by an external dc magnet. The magneticfield produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magneticfield which supplements that of the dc magnet so that when the fast magnet is energized the combined magneticfield is now greater that the critical field and the superconducting material returns to its normal state allowing the magneticfield to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. 6 figs.

The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magneticfield which is produced by an external dc magnet. The magneticfield produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magneticfield which supplements that of the dc magnet so that when the fast magnet is energized the combined magneticfield is now greater that the critical field and the superconducting material returns to its normal state allowing the magneticfield to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles.

Mars possesses no dynamic magneticfield of internal origin as it is the case for the Earth or for Mercury. Instead Mars is characterized by an intense and localized magneticfield of crustal origin. This field is the result of past magnetization and demagnetization processes, and reflects its evolution. The Interplanetary MagneticField (IMF) interacts with Mars' ionized environment to create an external magneticfield. This external field is weak compared to lithospheric one but very dynamic, and may hamper the detailed analysis of the internal magneticfield at some places or times. Because there are currently no magneticfield measurements made at Mars' surface, it is not possible to directly monitor the external field temporal variability as it is done in Earth's ground magnetic observatories. In this study we examine to indirect ways of quantifying this external field. First we use the Advanced Composition Explorer (ACE) mission which measures the solar wind about one hour upstream of the bow-shock resulting from the interaction between the solar wind and the Earth's internal magneticfield. These measurements are extrapolated to Mars' position taking into account the orbital configurations of the Mars-Earth system and the velocity of particles carrying the IMF. Second we directly use Mars Global Surveyor magneticfield measurements to quantify the level of variability of the external field. We subtract from the measurements the internal field which is otherwise modeled, and bin the residuals first on a spatial and then on a temporal mesh. This allows to compute daily or semi daily index. We present a comparison of these two proxies and demonstrate their complementarity. We also illustrate our analysis by comparing our Martian external field proxies to terrestrial index at epochs of known strong activity. These proxies will especially be useful for upcoming magneticfield measurements made around or at the surface of Mars.

Fe3O4 has been widely studied because of its great potential in spintronics and other applications. As a magnetic electrode, it is highly desired if magneticanisotropy can be controlled. Here, we report the results from our systematic study on the magnetic properties of magnetite (Fe3O4) thin films epitaxially grown on various MgO substrates. Strikingly, we observed a prominent perpendicular magneticanisotropy in Fe3O4 film deposited on MgO (111) substrate. When measured in out-of-plane direction, the film (40 nm thick) exhibits a well-defined square hysteresis loop with coercivity (Hc) above 1 kOe, while much lower coercivity was obtained in the in-plane orientation. In sharp contrast, the films deposited onto MgO (100) and MgO (110) substrates show in-plane magneticanisotropy. These films exhibit a typical soft magnet characteristicHc lies within the range of 200-400 Oe. All the films showed a clear Verwey transition near 120 Ka characteristic of Fe3O4 material. In addition, a series of magnetoresistance (MR) measurements is performed and the MR results are in good agreement with the magnetic observations. The role of the substrate orientation and film thickness dependency is also investigated.

During IODP Expedition 318, Sites U1359 and U1361 were drilled on the continental rise offshore the Wilkes Subglacial Basin to reconstruct the stability of the East Antarctic Ice Sheet (EAIS) during Neogene warm periods, such as the late Miocene and the early Pliocene. As the drilled core contains a complex history of compaction, erosion (thus hiatuses), and likely artificial disturbances, identifying these is important for reconstructing paleoenvironments. Anisotropy of magnetic susceptibility (AMS) is sensitive to lithological changes and differential compaction. At both sites, highly anisotropic layers correspond with turbidite units, lithologic boundaries and hiatuses. In places, it appears that low anisotropy is controlled by the bioturbated units and high productivity layers. Here we present a detailed study of the relationships between sediment compaction, based on AMS fabric variations in sedimentary records, and magnetic mineralogy. A clear correlation can be found between the degree of anisotropy and moisture content and diatom abundance during the Pliocene, but this pattern breaks down in the late Miocene. There are also strong rock magnetic indications for changes in the sources of the magnetic minerals throughout the Miocene to Pliocene. Furthermore, a significant difference exists between magnetic minerals at Sites U1359 and U1361. We will use our AMS and rock magnetic study to 1) characterize sediment compaction with biological productivity, and 2) detect the source of magnetic mineralogy throughout the late Miocene to Pliocene at both sites.

Py/FeMn/Cu(001) and Py/FeMn/Ni/Cu(001) films were grown and studied as a function of both the FeMn and the Ni thicknesses using rotating magneto-optic Kerr effect and x-ray magnetic circular dichroism. For Py/FeMn/Cu(001), we find that the FeMn antiferromagnetic order switches the sign of the Py fourfold magneticanisotropy but has little effect on the step-induced uniaxial magneticanisotropy. For Py/FeMn/Ni/Cu(001), we find that out-of-plane Ni magnetization has little effect on the Py magneticanisotropy, but in-plane Ni magnetization enhances the Py magneticanisotropy in the region just above antiferromagnetic transition thickness. The underlying mechanism could be attributed to the FeMn 3Q spin structure.

Spin-orbit torques are studied in Ta/TbFeCo/MgO patterned structures, where the ferrimagnetic material TbFeCo provides a strong bulk perpendicular magneticanisotropy (bulk-PMA) independent of the interfaces. The current-induced magnetization switching in TbFeCo is investigated in the presence of a perpendicular, longitudinal, or transverse field. An unexpected partial-switching phenomenon is observed in the presence of a transverse field unique to our bulk-PMA material. It is found that the anti-damping torque related with spin Hall effect is very strong, and a spin Hall angle is determined to be 0.12. The field-like torque related with Rashba effect is unobservable, suggesting that the interface play a significant role in Rashba-like torque.

A method of measuring the first magneticanisotropy constant, K1, of cubic crystals having a large anisotropy was developed which utilized measurements of the torque for directions of the applied field near the direction of easy magnetization. By this method K1 of a cobalt ferrite crystal was found to be closely approximated by the empirical relationship K1=19.6×106 exp(-1.90×10- 5T2) ergs\\/cc

The magneticfield of the solar corona evolves quasistatically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. We show that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, we calculate the equilibrium of a thin magnetic flux tube with small twist per unit length.

We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4?Å to 14?Å. For the iron deposited at 140?K, we obtained perpendicular magnetization at room temperature below the critical thickness of t{sub c}?=?(9?±?1)?Å. In the vicinity of t{sub c}, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to t{sub c}.

In this study, a new magneticfield flow fractionation (FFF) system was designed and modeled by using finite element simulations. Other than current magnetic FFF systems, which use static magneticfields, our system uses cyclical magneticfields. Results of the simulations show that our cyclical magnetic FFF system can be used effectively for the separation of magnetic nanoparticles. Cyclical magnetic FFF system is composed of a microfluidic channel (length = 5 cm, height = 30 ?m) and 2 coils. Square wave currents of 1 Hz (with 90 deg of phase difference) were applied to the coils. By using Comsol Multiphysics 3.5a, magneticfield profile and corresponding magnetic force exerted on the magnetite nanoparticles were calculated. The magnetic force data were exported from Comsol to Matlab. In Matlab, a parabolic flow profile with maximum flow speed of 0.4 mL/h was defined. Particle trajectories were obtained by the calculation of the particle speeds resulted from both magnetic and hydrodynamic forces. Particle trajectories of the particles with sizes ranging from 10 to 50 nm were simulated and elution times of the particles were calculated. Results show that there is a significant difference between the elution times of the particles so that baseline separation of the particles can be obtained. In this work, it is shown that by the application of cyclical magneticfields, the separation of magnetic nanoparticles can be done efficiently.

Magneticanisotropy in sedimentary rocks is controlled by the processes of deposition and compaction, in volcanic rocks by the lava flow and in metamorphic and plutonic rocks by ductile deformation and mimetic crystallization. In massive ore it is due to processes associated with emplacement and consolidation of an ore body as well as to ductile deformation. Hence, it can be

We present a Monte Carlo simulation of a model of a thin film consisting of a two-dimensional square lattice of classical Heisenberg spins with perpendicular anisotropy, short-range exchange and long-range dipolar interactions with the aim to explain the dependence on the magnetic history of the in-plane to out-of-plane reorientation transition observed in experiments.

Magnetic thin films and nanostructure exhibit novel properties and have great technological potential. In particular, developing thin film structures with perpendicular anisotropy, understanding the underlying mechanisms and identifying meaningful microstructure-property relationships in such nanometer scale materials is an ongoing challenge. Here, two different approaches as well as details of the relevant microstructure are presented. 6 refs, 2 figs.

Ordered arrays of CoxNi1-x nanowires (0anisotropy axis, which is determined by the balance between the hcp and fcc magnetocrystalline and shape anisotropies. We report on the nanowires structural and magnetic properties (e.g., hysteresis curves and their parameters as well as first-order reversal curve analysis), paying particular attention to their angular dependence. It is confirmed that the crystal phase of nanowires with length 2.5 ?m and diameter 35 nm shifts from hcp to fcc as the Ni content increases. That results in a significant modification of the magnetization process and, accordingly, of the magnetic properties of the array. Analytical calculations of the angular dependence of the coercivity allow us to confirm that the magnetization reversal is mostly ascribed to the propagation of a transverse domain wall. Fitting of the experiment to these calculations indicates the presence of a transverse crystalline anisotropy (ascribed to the hcp phase) in Co wires, while this changes to an axial anisotropy (fcc phase) as the Ni content increases.

Magneticfield fluctuations at the betatron frequency can lead to emittance growth in circular accelerators. Tolerances are extremely tight for large hadron colliders like LHC and VLHC[1]. We performed experimental studies of the fluctuations in a stand-alone superconducting Tevatron magnet. Here we give a general description of the experimental set-up, present main results and discuss consequences for the colliders.

The powerful magneticfields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magneticfields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magneticfields. An overview of the results of past research into the bioeffects of magneticfields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

A device is provided for measuring the magneticfield dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magneticfield and associated electronics for data storage, calculating, retrieving and display.

Magnetic nanoparticles (MNPs) are extensively used in biotechnology. These applications rely on magnetic properties that are a keen function of MNP size, distribution, and shape. Various magneto-optical techniques, including Faraday Rotation (FR), Cotton-Mouton Effect, etc., have been employed to characterize magnetic properties of MNPs. Generally, these measurements employ AC or DC fields. In this work, we describe the results from a FR setup that uses pulsed magneticfields and an analysis technique that makes use of the entire pulse shape to investigate size distribution and shape anisotropy. The setup employs a light source, polarizing components, and a detector that are used to measure the rotation of light from a sample that is subjected to a pulsed magneticfield. This magneticfield "snapshot" is recorded alongside the intensity pulse of the sample's response. This side by side comparison yields useful information about the real time magnetization dynamics of the system being probed. The setup is highly flexible with variable control of pulse length and peak magnitude. Examining the raw data for the response of bare Fe3O4 and hybrid Au and Fe3O4 nanorods reveals interesting information about Brownian relaxation and the hydrodynamic size of these nanorods. This analysis exploits the self-referencing nature of this measurement to highlight the impact of an applied field on creating a field induced transparency for a longitudinal measurement. Possible sources for this behavior include shape anisotropy and field assisted aggregate formation.

Magnetic metallic multilayers separated by nonmagnetic metal films are of great importance in magnetoelectronics and spintronics, due to their capacity of giving rise to giant magneto-resistance as well as the electric field control of ferromagnetism. Co/Pt multilayers are one of the typical platforms that own perpendicular magneticanisotropy which can be tuned in various ways. Since previous investigations focus on the anomalous Hall(transverse) resistivity which characterizes the magnetization of the multilayers, much less attention has been paid to the longitudinal resistivity. In this work, we find that the longitudinal resistivity also gives rich phenomena that need further theoretical treatment. We have grown two Co/Pt multilayer structures that have different spacings between neighboring ferromagnetic layers. The one with smaller spacing shows a superparamagnetic behavior in its Hall resistivity even at a temperature as low as 1.5 K, but the longitudinal resistivity shows a well established hysteresis. The other sample shows square hysteresis in the Hall resistivity at all available temperatures up to 300 K, while the longitudinal resistivity gives no significant signals because they are mostly engulfed in the noises. The corresponding temperature dependence of the coercive field are also different. While the former gives an approximately exponential function of the temperature T, the latter can be divided to two zones, each of which can be characterized by a lnTs dependence, where s is not necessarily an integer. Such distinct features may be deeply related to the microstructures as well as the magnon scattering, which require further investigations.

(Revised December 30, 2013) MagneticFields GOALS (1) To visualize the magneticfields produced compasses to trace out the magneticfield lines of a single bar magnet on a large sheet of paper. (3 of the points where the magneticfields of the Earth and the bar magnet sum to zero. INTRODUCTION A magnetic

Polycrystalline and epitaxial (100), (110), and (111)-oriented Ni3Pt, NiPt, and NiPt3 films were deposited over a range of growth temperatures from 80°C to 700°C. Films grown at moderate temperatures (200400°C) exhibit growth-induced properties similar to CoPt alloys: enhanced and broadened Curie temperature, perpendicular magneticanisotropy and large coercivity. As in CoPt, the magnetic properties suggest a clustering of Ni into

The Beaver River Diabase (BRD) is a series of mafic dikes and sills within the Beaver Bay Complex (BBC) of northern Minnesota, which formed during the development of the ~1.1 Ga Midcontinent Rift (MCR). The BRD is one of the youngest and most extensive intrusive phases of the BBC. The BRD dikes and sills were emplaced into the medial levels of the 6-10 kilometer-thick North Shore Volcanic Group and occur over an arcuate area extending 120 by 20 kilometers. The BRD is composed of fine- to medium-grained ophitic olivine gabbro and does not display obvious foliation or lineation features and rarely displays modal layering. Without obvious magmatic internal structures, it is difficult to determine emplacement properties such as flow direction using standard geologic mapping or petrographic techniques. For this reason, we measured the anisotropy of magnetic susceptibility (AMS), in conjunction with other rock magnetic properties, to better understand the BRD's emplacement and deformation history in the context of the MCR. AMS measures the directional dependence of low-fieldmagnetic susceptibility, and is used to infer a shape-preferred orientation of magnetic minerals within a rock, which can be related to specific emplacement mechanisms (e.g. directional flow or settling). Preliminary analysis of AMS at 20 sites within the southern half of the BRD (with 4-7 samples per site) shows maximum susceptibility values between 4.48 x 10-6 and 2.22 x 10-4 m3/kg (1165 and 65400 ?SI). Most specimens display nearly isotropic AMS ellipsoids (Pj < 1.15) with minor degrees of prolateness and oblateness. However, about 20% of specimens have higher anisotropies (Pj between 1.15 and 1.67) and higher degrees of oblateness and prolateness. Variations in AMS properties may reflect differences in concentration and composition, as well as emplacement mechanisms. Measurements of susceptibility as a function of temperature yield Curie points between 470 and 570 °C, indicating a presence of low-titanium titanomagnetite. Major hysteresis loops and first order reversal curve (FORC) experiments show coercivities between 1 and 125 mT, with a bulk average microcoercivity of 25 mT, consistent with titanomagnetite as the dominant remanence carrier. Further analysis will also investigate the relationship of AMS to rock fabric by measuring mineral crystal preferred orientations using electron backscatter diffraction. These measurements will supplement the AMS data, and provide links to the role of microstructure, texture and mineralogy in AMS.

We have prepared the dilute magnetic semiconductor (DMS) InMnAs with different Mn concentrations by ion implantation and pulsed laser melting. The Curie temperature of the In1?xMnxAs epilayer depends on the Mn concentration x, reaching 82?K for x = 0.105. The substitution of Mn ions at the indium sites induces a compressive strain perpendicular to the InMnAs layer and a tensile strain along the in-plane direction. This gives rise to a large perpendicular magneticanisotropy, which is often needed for the demonstration of the electrical control of magnetization and for spin-transfer-torque induced magnetization reversal.

The efficiency of different mechanisms of sunspot magneticfield dissipation depending on the stage of sunspot decay and optical depth is investigated. The highest rate of the magneticfield diffusion has place at the initial stage of sunspot decay, when the turbulence motion in the sunspot umbra takes a two-dimensional structure due to the strong magneticfield (B ? 3000 G). The turbulence degeneracy withdraws at the later stage of the sunspot decay (B ? 2000 G) and the dissipation slows down.

We examine the distribution of the magneticanisotropy experienced by a magnetic impurity embedded in a metallic nanograin. As an example of a generic magnetic impurity with a partially filled d shell, we study the case of d1 impurities embedded into ordered and disordered Au nanograins, described in terms of a realistic band structure. Confinement of the electrons induces a magneticanisotropy that is large, and can be characterized by five real parameters, coupling to the quadrupolar moments of the spin. In ordered (spherical) nanograins, these parameters exhibit symmetrical structures and reflect the symmetry of the underlying lattice, while for disordered grains they are randomly distributed and, for stronger disorder, their distribution is found to be characterized by random matrix theory. As a result, the probability of having small magneticanisotropies KL is suppressed below a characteristic scale ?E, which we predict to scale with the number of atoms N as ?E1 /N3 /2 . This gives rise to anomalies in the specific heat and the susceptibility at temperatures T ?E and produces distinct structures in the magnetic excitation spectrum of the clusters that should be possible to detect experimentally.

A vertically draining thin ferrofilm under the influence of gravity and a nonuniform magneticfield is considered. It is observed experimentally that the presence of the magneticfield greatly alters the drainage of the film. A mathematical model is developed to describe the behavior. Experiments are conducted for multiple magneticfield configurations. The model is solved for two different sets of boundary conditions and results are compared to experiments. It is shown that the magneticfield structure, the concentration of magnetite in the solution, and the boundary conditions all have noticeable affects on the evolution of the thinning film. Good qualitative agreement between the model and the experiments is observed.

Transcranial magnetic stimulation (TMS) can be used for evaluating the function of motor pathways. According to the principles of electromagnetism and electrophysiology, TMS activates those neurons that are suitably oriented with respect to the TMS-induced electric field. We hypothesized that TMS could potentially be able to evaluate the neuronal structure, although until now, this putative application has not been exploited. We have developed a TMS-based method to evaluate the function and structure of the motor cortex concurrently in a quantitative manner. This method produced a measure, the anisotropy index (AI), which is based on the motor-evoked potentials induced at different coil orientations. The AI was demonstrated to exhibit an association with both motor cortex excitability and neuronal structure. In the present study, we evaluated the repeatability (intrasession and intersession) of AI in three consecutive measurements. In addition, we studied the repeatability of the optimal coil angle in inducing motor-evoked potentials. Two of the measurements were conducted on the same stimulation target and the third on a remapped target. The coefficient of repeatability of the AI was 0.022 for intrasession and 0.040 for intersession assessments. For the optimal stimulation angle, the coefficients of repeatability were 3.7° and 5.1°, respectively. Both the AI and the optimal stimulation angle demonstrated good repeatability (Cronbach's ?>0.760). In conclusion, the results indicate that the AI can provide a reliable estimation of local functional anisotropy changes under conditions affecting the cortex, such as during stroke or focal dysplasia. PMID:26011386

In the RCo5 compounds with trivalent R atoms, cobalt magnetism is well established. When R atoms are tetravalent (Th, Ce), the onset of 3d magnetism occurs through metamagnetism of collective electrons. This behaviour results from 3d-6d (or 5d) hybridization. The exceptionally large magnetocrystalline anisotropy of cobalt in these RCo5 compounds is due to a large orbital contribution to the cobalt

Our present-day understanding of solar and stellar magneticfields is discussed from both an observational and theoretical viewpoint. To begin with, observations of the Sun's large-scale magneticfield are described, along with recent advances in measuring the spatial distribution of magneticfields on other stars. Following this, magnetic flux transport models used to simulate photospheric magneticfields and the wide variety of techniques used to deduce global coronal magneticfields are considered. The application and comparison of these models to the Sun's open flux, hemispheric pattern of solar filaments and coronal mass ejections are then discussed. Finally, recent developments in the construction of steady-state global magnetohydrodynamic models are considered, along with key areas of future research. PMID:22665897

The anisotropy, D\\/\\/\\/D?, of water diffusion in fully hydrated bilayers of dimyristoylphosphatidylcholine at 29°C has been measured by pulsed magneticfield gradient (pfg) NMR. By using NMR imaging hardware to produce magneticfield gradients in an arbitrary direction with respect to a stack of macroscopically aligned lipid bilayers, translational diffusion of water was measured as a function of the angle

A number of mechanisms, such as magneticfields, (binary) companions and circumstellar disks have been suggested to be the cause of non-spherical PNe and in particular collimated outflows. This work investigates one of these mechanisms: the magneticfields. While MHD simulations show that the fields can indeed be important, few observations of magneticfields have been done so far. We used the VLBA to observe five evolved stars, with the goal of detecting the magneticfield by means of water maser polarization. The sample consists in four AGB stars (IK Tau, RT Vir, IRC+60370 and AP Lyn) and one pPN (OH231.8+4.2). In four of the five sources, several strong maser features were detected allowing us to measure the linear and/or circular polarization. Based on the circular polarization detections, we infer the strength of the component of the field along the line of sight to be between ~30 mG and ~330 mG in the water maser regions of these four sources. When extrapolated to the surface of the stars, the magneticfield strength would be between a few hundred mG and a few Gauss when assuming a toroidal field geometry and higher when assuming more complex magneticfields. We conclude that the magnetic energy we derived in the water maser regions is higher than the thermal and kinetic energy, leading to the conclusion that, indeed, magneticfields probably play an important role in shaping Planetary Nebulae.

It is well known that axial magneticfields (AMFs) can keep vacuum arc in diffuse mode at high current. According to our recent research and other published papers, it has been found that vacuum arc can be maintained in high-current diffuse mode at much higher current if nonuniform AMF is applied, that the axial magneticfield is higher at contact

The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and Ni-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials. A brief summary of work done in each area is given.

We present a method to preselect the direction of an induced in-plane uniaxial magneticanisotropy (UMA) in thin single-crystalline Fe films on MgO(001). Ion beam irradiation is used to modulate the MgO(001) surface with periodic ripples on the nanoscale. The ripple direction determines the orientation of the UMA, whereas the intrinsic cubic anisotropy of the Fe film is not affected. Thus, it is possible to superimpose an in-plane UMA with a precision of a few degreesa level of control not reported so far that can be relevant for example in spintronics.